<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:be65e6e5-8ffc-47c3-ba79-c75d0794ccd3,g:cf638115-0f9d-4e49-bfff-bc41e206a04e-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.ul.com/role/Cover" xlink:type="simple" xlink:href="uls-20250331.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_6d03375a-dbaa-48f4-b068-0ae0a02d3303" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntitiesTable_6d03375a-dbaa-48f4-b068-0ae0a02d3303" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_7e6c7337-bfcf-4b38-b258-f9c3bc77b253" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_6d03375a-dbaa-48f4-b068-0ae0a02d3303" xlink:to="loc_us-gaap_StatementClassOfStockAxis_7e6c7337-bfcf-4b38-b258-f9c3bc77b253" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_7e6c7337-bfcf-4b38-b258-f9c3bc77b253_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_7e6c7337-bfcf-4b38-b258-f9c3bc77b253" xlink:to="loc_us-gaap_ClassOfStockDomain_7e6c7337-bfcf-4b38-b258-f9c3bc77b253_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_711e52a1-83e9-4fc5-922c-8a1db90e1633" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_7e6c7337-bfcf-4b38-b258-f9c3bc77b253" xlink:to="loc_us-gaap_ClassOfStockDomain_711e52a1-83e9-4fc5-922c-8a1db90e1633" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_2c5df2ae-50fd-4aa8-b226-67994a76fa44" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_711e52a1-83e9-4fc5-922c-8a1db90e1633" xlink:to="loc_us-gaap_CommonClassAMember_2c5df2ae-50fd-4aa8-b226-67994a76fa44" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_17472cd6-1bc3-4ec9-ae3a-b4bd6c30ba14" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_711e52a1-83e9-4fc5-922c-8a1db90e1633" xlink:to="loc_us-gaap_CommonClassBMember_17472cd6-1bc3-4ec9-ae3a-b4bd6c30ba14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_bc5c0a04-236f-4e6d-afc0-6ebb07cafc7a" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_DocumentType_bc5c0a04-236f-4e6d-afc0-6ebb07cafc7a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_c46d21d7-a1ab-4267-9398-9898527237e0" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_DocumentQuarterlyReport_c46d21d7-a1ab-4267-9398-9898527237e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_7ce3af93-7923-416d-8426-b86d8f0e4cba" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_DocumentPeriodEndDate_7ce3af93-7923-416d-8426-b86d8f0e4cba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_38b53a93-0a41-4b13-aafc-547d25c0caa5" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_DocumentTransitionReport_38b53a93-0a41-4b13-aafc-547d25c0caa5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_3d27b428-2763-4cf2-9a5a-6bfcb30f684d" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityFileNumber_3d27b428-2763-4cf2-9a5a-6bfcb30f684d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_03e248fe-d438-480b-b5bf-a6eda3657eb5" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityRegistrantName_03e248fe-d438-480b-b5bf-a6eda3657eb5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_edea6f60-c016-463f-8bf0-f7a386184fa0" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityIncorporationStateCountryCode_edea6f60-c016-463f-8bf0-f7a386184fa0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_1d754384-f03e-4bf2-b0a8-706de798d3ce" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityTaxIdentificationNumber_1d754384-f03e-4bf2-b0a8-706de798d3ce" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_a186b4c7-0be7-4388-ae94-aa4d69c366c0" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityAddressAddressLine1_a186b4c7-0be7-4388-ae94-aa4d69c366c0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_5853ebda-5940-4e2d-84ce-a4698cfb1a89" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityAddressCityOrTown_5853ebda-5940-4e2d-84ce-a4698cfb1a89" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_e14c3b9b-ea0e-4082-b396-a0aa7f89e7b8" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityAddressStateOrProvince_e14c3b9b-ea0e-4082-b396-a0aa7f89e7b8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_3b91078e-022e-40ce-8f03-094cc9b766f0" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityAddressPostalZipCode_3b91078e-022e-40ce-8f03-094cc9b766f0" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_ef1b407e-3cab-4d98-84dc-0133ae14f9e0" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_CityAreaCode_ef1b407e-3cab-4d98-84dc-0133ae14f9e0" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_c3535bd1-f2c2-4869-bea1-04af323e20e0" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_LocalPhoneNumber_c3535bd1-f2c2-4869-bea1-04af323e20e0" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_0ece3d9a-ec6b-4907-a559-fc605fae01e1" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_Security12bTitle_0ece3d9a-ec6b-4907-a559-fc605fae01e1" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_4296521b-b40a-4744-968d-9375eb9bff9a" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_TradingSymbol_4296521b-b40a-4744-968d-9375eb9bff9a" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_56e3fa32-0bba-4bc6-b3c2-f1e016fcb2b8" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_SecurityExchangeName_56e3fa32-0bba-4bc6-b3c2-f1e016fcb2b8" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_47cbd326-0f12-4745-852f-57275733d976" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityCurrentReportingStatus_47cbd326-0f12-4745-852f-57275733d976" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_2a99a190-4023-460b-8c7d-243726ab4f25" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityInteractiveDataCurrent_2a99a190-4023-460b-8c7d-243726ab4f25" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_13e421f3-2612-476f-8860-b45cccfd8ccb" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityFilerCategory_13e421f3-2612-476f-8860-b45cccfd8ccb" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_4e35255f-1df8-4a2a-92cc-ead4ba052376" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntitySmallBusiness_4e35255f-1df8-4a2a-92cc-ead4ba052376" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_2a7dd90e-b0b6-4802-b4d2-4c2341e51735" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityEmergingGrowthCompany_2a7dd90e-b0b6-4802-b4d2-4c2341e51735" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_3bdcbb0f-fc26-4a12-a57f-d427f3ef75d4" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityShellCompany_3bdcbb0f-fc26-4a12-a57f-d427f3ef75d4" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_a6fbc9ad-2532-447d-bcf7-9d016c181178" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_a6fbc9ad-2532-447d-bcf7-9d016c181178" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_72bb384b-1bac-40a7-801a-e6f49a3b2fcc" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_EntityCentralIndexKey_72bb384b-1bac-40a7-801a-e6f49a3b2fcc" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_cea15004-1e30-4e75-b7a3-834f2cc04ab9" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_CurrentFiscalYearEndDate_cea15004-1e30-4e75-b7a3-834f2cc04ab9" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_b6c68f1d-0789-4ac6-9825-acdb3cf97cad" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_DocumentFiscalYearFocus_b6c68f1d-0789-4ac6-9825-acdb3cf97cad" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_abaa5eac-0aaa-45db-adab-5ed8f250dca9" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_DocumentFiscalPeriodFocus_abaa5eac-0aaa-45db-adab-5ed8f250dca9" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_e1269155-6731-4335-af15-ba3ceafde107" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_b4b0bb66-e96a-4c14-b200-73d5047672dc" xlink:to="loc_dei_AmendmentFlag_e1269155-6731-4335-af15-ba3ceafde107" xlink:type="arc" order="28"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/CondensedConsolidatedBalanceSheets" xlink:type="simple" xlink:href="uls-20250331.xsd#CondensedConsolidatedBalanceSheets"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/CondensedConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_7d88fd04-5bfa-44d6-b32f-396eee333527" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_f90c25b3-2cff-4d3a-a5ce-55de75e1b22d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_7d88fd04-5bfa-44d6-b32f-396eee333527" xlink:to="loc_us-gaap_StatementTable_f90c25b3-2cff-4d3a-a5ce-55de75e1b22d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_d4aab197-d5fb-44dc-a710-d38aabbe3293" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_f90c25b3-2cff-4d3a-a5ce-55de75e1b22d" xlink:to="loc_us-gaap_StatementClassOfStockAxis_d4aab197-d5fb-44dc-a710-d38aabbe3293" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_d4aab197-d5fb-44dc-a710-d38aabbe3293_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_d4aab197-d5fb-44dc-a710-d38aabbe3293" xlink:to="loc_us-gaap_ClassOfStockDomain_d4aab197-d5fb-44dc-a710-d38aabbe3293_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9f084d0c-aa4a-427e-98a4-24e6d3454a5e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_d4aab197-d5fb-44dc-a710-d38aabbe3293" xlink:to="loc_us-gaap_ClassOfStockDomain_9f084d0c-aa4a-427e-98a4-24e6d3454a5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_51f969e8-fcf5-4672-9a1e-f7288fd1f589" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9f084d0c-aa4a-427e-98a4-24e6d3454a5e" xlink:to="loc_us-gaap_CommonClassAMember_51f969e8-fcf5-4672-9a1e-f7288fd1f589" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_78470349-ca53-4c26-a67a-634b45b9b385" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9f084d0c-aa4a-427e-98a4-24e6d3454a5e" xlink:to="loc_us-gaap_CommonClassBMember_78470349-ca53-4c26-a67a-634b45b9b385" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_756dfda5-bae2-4081-8379-4a5e6f835cae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7d88fd04-5bfa-44d6-b32f-396eee333527" xlink:to="loc_us-gaap_AssetsAbstract_756dfda5-bae2-4081-8379-4a5e6f835cae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_c4f0a658-4616-40b6-9c86-12d62afd3cca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_756dfda5-bae2-4081-8379-4a5e6f835cae" xlink:to="loc_us-gaap_AssetsCurrentAbstract_c4f0a658-4616-40b6-9c86-12d62afd3cca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_109c9b8e-05aa-4132-bf1b-94e44d950ac2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_c4f0a658-4616-40b6-9c86-12d62afd3cca" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_109c9b8e-05aa-4132-bf1b-94e44d950ac2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_ca10c4ef-fbb3-482f-89a9-f9190e868bf6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_c4f0a658-4616-40b6-9c86-12d62afd3cca" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_ca10c4ef-fbb3-482f-89a9-f9190e868bf6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_96a9d04f-a452-4ccd-9d7a-67d406a9e436" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerAssetNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_c4f0a658-4616-40b6-9c86-12d62afd3cca" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_96a9d04f-a452-4ccd-9d7a-67d406a9e436" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_b65b0e2f-ed89-46e8-a2d9-2498c21c9068" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_c4f0a658-4616-40b6-9c86-12d62afd3cca" xlink:to="loc_us-gaap_OtherAssetsCurrent_b65b0e2f-ed89-46e8-a2d9-2498c21c9068" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_25a82156-ac88-494c-9ed5-ab38f57567c1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_c4f0a658-4616-40b6-9c86-12d62afd3cca" xlink:to="loc_us-gaap_AssetsCurrent_25a82156-ac88-494c-9ed5-ab38f57567c1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_3f860f83-3877-40fe-a9af-08152626f685" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_756dfda5-bae2-4081-8379-4a5e6f835cae" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_3f860f83-3877-40fe-a9af-08152626f685" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_62b69910-295d-41b2-8c52-f07762d90fa4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_756dfda5-bae2-4081-8379-4a5e6f835cae" xlink:to="loc_us-gaap_Goodwill_62b69910-295d-41b2-8c52-f07762d90fa4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_312e15b5-f0c7-47dd-836f-9030aab1e450" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_756dfda5-bae2-4081-8379-4a5e6f835cae" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_312e15b5-f0c7-47dd-836f-9030aab1e450" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_01b80f70-93a8-4504-a32d-5424b1ffa0eb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_756dfda5-bae2-4081-8379-4a5e6f835cae" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_01b80f70-93a8-4504-a32d-5424b1ffa0eb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxAssetsNet_da7db4e1-8af0-4389-b0b1-feaa2ca5c97f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredIncomeTaxAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_756dfda5-bae2-4081-8379-4a5e6f835cae" xlink:to="loc_us-gaap_DeferredIncomeTaxAssetsNet_da7db4e1-8af0-4389-b0b1-feaa2ca5c97f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedComputerSoftwareNet_60a1760e-cd5d-4ac5-a9f6-90b7a6073bd0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CapitalizedComputerSoftwareNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_756dfda5-bae2-4081-8379-4a5e6f835cae" xlink:to="loc_us-gaap_CapitalizedComputerSoftwareNet_60a1760e-cd5d-4ac5-a9f6-90b7a6073bd0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_f2954771-0c83-4043-b647-b11f3b0e2376" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_756dfda5-bae2-4081-8379-4a5e6f835cae" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_f2954771-0c83-4043-b647-b11f3b0e2376" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_50d4d603-be04-4c76-85ce-ac6531e60452" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_756dfda5-bae2-4081-8379-4a5e6f835cae" xlink:to="loc_us-gaap_Assets_50d4d603-be04-4c76-85ce-ac6531e60452" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5a6772df-3563-4345-a323-8105b338d4fb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7d88fd04-5bfa-44d6-b32f-396eee333527" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5a6772df-3563-4345-a323-8105b338d4fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_dd18b316-9cce-4cf6-9b11-0ba26949daf1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5a6772df-3563-4345-a323-8105b338d4fb" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_dd18b316-9cce-4cf6-9b11-0ba26949daf1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_fa89a739-f274-4344-8f48-fd8d36b9870a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_dd18b316-9cce-4cf6-9b11-0ba26949daf1" xlink:to="loc_us-gaap_LongTermDebtCurrent_fa89a739-f274-4344-8f48-fd8d36b9870a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_7f9eee5b-1b4b-442d-b032-241c3bfab645" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_dd18b316-9cce-4cf6-9b11-0ba26949daf1" xlink:to="loc_us-gaap_AccountsPayableCurrent_7f9eee5b-1b4b-442d-b032-241c3bfab645" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_2e2f5a89-b5e5-4043-a2b1-38fb192cdd05" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_dd18b316-9cce-4cf6-9b11-0ba26949daf1" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_2e2f5a89-b5e5-4043-a2b1-38fb192cdd05" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_56a2162e-9a4f-435f-a569-21f5f1d63c18" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_dd18b316-9cce-4cf6-9b11-0ba26949daf1" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_56a2162e-9a4f-435f-a569-21f5f1d63c18" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_54e39d51-54a8-463b-904c-1ea5eb66f7a6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_dd18b316-9cce-4cf6-9b11-0ba26949daf1" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_54e39d51-54a8-463b-904c-1ea5eb66f7a6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_f508cc35-1e88-4edf-9526-a5c5668a120c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_dd18b316-9cce-4cf6-9b11-0ba26949daf1" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_f508cc35-1e88-4edf-9526-a5c5668a120c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_48e64989-6c95-48bf-8492-60baddaaac0d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_dd18b316-9cce-4cf6-9b11-0ba26949daf1" xlink:to="loc_us-gaap_LiabilitiesCurrent_48e64989-6c95-48bf-8492-60baddaaac0d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_2268f410-279c-4e7b-8f5c-991976256d31" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5a6772df-3563-4345-a323-8105b338d4fb" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_2268f410-279c-4e7b-8f5c-991976256d31" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_fbf2bd4f-cc0f-4a9c-9049-665b5287bd19" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5a6772df-3563-4345-a323-8105b338d4fb" xlink:to="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_fbf2bd4f-cc0f-4a9c-9049-665b5287bd19" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_4b4ed975-8818-4bf3-b404-8af0e47fbb6d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5a6772df-3563-4345-a323-8105b338d4fb" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_4b4ed975-8818-4bf3-b404-8af0e47fbb6d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_dd68d744-995f-45b0-a2d0-529d4b29e4c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5a6772df-3563-4345-a323-8105b338d4fb" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_dd68d744-995f-45b0-a2d0-529d4b29e4c5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_c29dedab-ec58-4589-948d-ae832efd05c9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5a6772df-3563-4345-a323-8105b338d4fb" xlink:to="loc_us-gaap_Liabilities_c29dedab-ec58-4589-948d-ae832efd05c9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_ed02a301-fabf-43d1-b9c4-e908276c501a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5a6772df-3563-4345-a323-8105b338d4fb" xlink:to="loc_us-gaap_CommitmentsAndContingencies_ed02a301-fabf-43d1-b9c4-e908276c501a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_42385181-b038-48e3-819f-f905d3b5e4c0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5a6772df-3563-4345-a323-8105b338d4fb" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_42385181-b038-48e3-819f-f905d3b5e4c0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_3330aaad-5248-4eae-af6b-9092a1ac7344" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_42385181-b038-48e3-819f-f905d3b5e4c0" xlink:to="loc_us-gaap_CommonStockValue_3330aaad-5248-4eae-af6b-9092a1ac7344" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_2ee0fa83-6c78-4f28-9fdb-b68a5d874804" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_42385181-b038-48e3-819f-f905d3b5e4c0" xlink:to="loc_us-gaap_AdditionalPaidInCapital_2ee0fa83-6c78-4f28-9fdb-b68a5d874804" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_442de9f6-8279-44d4-9a49-2e06baedd6dd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_42385181-b038-48e3-819f-f905d3b5e4c0" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_442de9f6-8279-44d4-9a49-2e06baedd6dd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_5cfcfeda-5dff-4d59-b7cb-1149e7087eb3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_42385181-b038-48e3-819f-f905d3b5e4c0" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_5cfcfeda-5dff-4d59-b7cb-1149e7087eb3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_03e9f2b7-ec02-4df6-adc3-9271a6f215ce" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_42385181-b038-48e3-819f-f905d3b5e4c0" xlink:to="loc_us-gaap_StockholdersEquity_03e9f2b7-ec02-4df6-adc3-9271a6f215ce" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterest_afe3df66-80e3-4abc-b50c-d5a9caedbe3d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MinorityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_42385181-b038-48e3-819f-f905d3b5e4c0" xlink:to="loc_us-gaap_MinorityInterest_afe3df66-80e3-4abc-b50c-d5a9caedbe3d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_c8056ea5-40d0-4b0f-8f75-9794370769dd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_42385181-b038-48e3-819f-f905d3b5e4c0" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_c8056ea5-40d0-4b0f-8f75-9794370769dd" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_4722d1c3-293e-4723-b230-fd860a035b26" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5a6772df-3563-4345-a323-8105b338d4fb" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_4722d1c3-293e-4723-b230-fd860a035b26" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="uls-20250331.xsd#CondensedConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_3faa2fd0-45ad-4370-afd3-16e7f35e76d7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_0b8e1736-8e2b-4dd9-83fa-841f36dde5f5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_3faa2fd0-45ad-4370-afd3-16e7f35e76d7" xlink:to="loc_us-gaap_StatementTable_0b8e1736-8e2b-4dd9-83fa-841f36dde5f5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_2925ba39-c2dc-4205-9483-c8344e3d9e98" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_0b8e1736-8e2b-4dd9-83fa-841f36dde5f5" xlink:to="loc_us-gaap_StatementClassOfStockAxis_2925ba39-c2dc-4205-9483-c8344e3d9e98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_2925ba39-c2dc-4205-9483-c8344e3d9e98_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_2925ba39-c2dc-4205-9483-c8344e3d9e98" xlink:to="loc_us-gaap_ClassOfStockDomain_2925ba39-c2dc-4205-9483-c8344e3d9e98_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_0a6d8cbd-4494-4023-a67b-9ca15b0d70ca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_2925ba39-c2dc-4205-9483-c8344e3d9e98" xlink:to="loc_us-gaap_ClassOfStockDomain_0a6d8cbd-4494-4023-a67b-9ca15b0d70ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_36c5d7b7-b9a4-449c-97e7-dbc63ea69c36" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_0a6d8cbd-4494-4023-a67b-9ca15b0d70ca" xlink:to="loc_us-gaap_CommonClassAMember_36c5d7b7-b9a4-449c-97e7-dbc63ea69c36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_389f5ef6-5be9-4e1d-ac99-6106d667e0d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_0a6d8cbd-4494-4023-a67b-9ca15b0d70ca" xlink:to="loc_us-gaap_CommonClassBMember_389f5ef6-5be9-4e1d-ac99-6106d667e0d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_7f1b67c0-5225-450d-b21e-f90e4a939934" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3faa2fd0-45ad-4370-afd3-16e7f35e76d7" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_7f1b67c0-5225-450d-b21e-f90e4a939934" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLossCurrent_aa7a4c84-3f5b-4186-b686-3947a273942e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLossCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3faa2fd0-45ad-4370-afd3-16e7f35e76d7" xlink:to="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLossCurrent_aa7a4c84-3f5b-4186-b686-3947a273942e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_393f9fa2-10f2-4986-a7a4-a74cfe252fb6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3faa2fd0-45ad-4370-afd3-16e7f35e76d7" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_393f9fa2-10f2-4986-a7a4-a74cfe252fb6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_015a0b2b-eea2-44be-8e06-509bedd7a60e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3faa2fd0-45ad-4370-afd3-16e7f35e76d7" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_015a0b2b-eea2-44be-8e06-509bedd7a60e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedComputerSoftwareAccumulatedAmortization_898cc4fb-10cb-4638-86f0-1bc30cc1bc39" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CapitalizedComputerSoftwareAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3faa2fd0-45ad-4370-afd3-16e7f35e76d7" xlink:to="loc_us-gaap_CapitalizedComputerSoftwareAccumulatedAmortization_898cc4fb-10cb-4638-86f0-1bc30cc1bc39" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_d02cb67f-45bf-4ce4-9868-e6742e6fa2ef" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3faa2fd0-45ad-4370-afd3-16e7f35e76d7" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_d02cb67f-45bf-4ce4-9868-e6742e6fa2ef" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_161ce7ff-6e4d-4483-8858-fd0ff9117933" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3faa2fd0-45ad-4370-afd3-16e7f35e76d7" xlink:to="loc_us-gaap_CommonStockSharesIssued_161ce7ff-6e4d-4483-8858-fd0ff9117933" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_79f7c19e-de52-4e96-85af-76e84b4377e9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3faa2fd0-45ad-4370-afd3-16e7f35e76d7" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_79f7c19e-de52-4e96-85af-76e84b4377e9" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="uls-20250331.xsd#CondensedConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_dd1db09e-df63-4fa6-9927-abbec6b3d3f1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_2a846eac-381e-4493-8250-7aae3270a3e1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_dd1db09e-df63-4fa6-9927-abbec6b3d3f1" xlink:to="loc_us-gaap_StatementTable_2a846eac-381e-4493-8250-7aae3270a3e1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_3ffc3035-c4c9-437c-a272-6a410868c3c1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_2a846eac-381e-4493-8250-7aae3270a3e1" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_3ffc3035-c4c9-437c-a272-6a410868c3c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_3ffc3035-c4c9-437c-a272-6a410868c3c1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_3ffc3035-c4c9-437c-a272-6a410868c3c1" xlink:to="loc_us-gaap_EquityComponentDomain_3ffc3035-c4c9-437c-a272-6a410868c3c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_49e6b351-2a7c-4fcd-bb3b-1d10d4bcfa9b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_3ffc3035-c4c9-437c-a272-6a410868c3c1" xlink:to="loc_us-gaap_EquityComponentDomain_49e6b351-2a7c-4fcd-bb3b-1d10d4bcfa9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_aa799427-42a2-4598-baf6-cd7b5c9f764a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_49e6b351-2a7c-4fcd-bb3b-1d10d4bcfa9b" xlink:to="loc_us-gaap_CommonStockMember_aa799427-42a2-4598-baf6-cd7b5c9f764a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_89d91cc8-df44-4a60-88f0-331928b0032a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_49e6b351-2a7c-4fcd-bb3b-1d10d4bcfa9b" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_89d91cc8-df44-4a60-88f0-331928b0032a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_0745b9db-d710-4860-8e2c-2a5c624f927c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_49e6b351-2a7c-4fcd-bb3b-1d10d4bcfa9b" xlink:to="loc_us-gaap_RetainedEarningsMember_0745b9db-d710-4860-8e2c-2a5c624f927c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_6762913c-5550-4b07-a0e7-47304f25defc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_49e6b351-2a7c-4fcd-bb3b-1d10d4bcfa9b" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_6762913c-5550-4b07-a0e7-47304f25defc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_78c3600b-5971-4650-9015-07f4bbd3075a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_49e6b351-2a7c-4fcd-bb3b-1d10d4bcfa9b" xlink:to="loc_us-gaap_NoncontrollingInterestMember_78c3600b-5971-4650-9015-07f4bbd3075a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_da0f9663-72d0-46a7-9e46-c5380b944eee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_dd1db09e-df63-4fa6-9927-abbec6b3d3f1" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_da0f9663-72d0-46a7-9e46-c5380b944eee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_2c29c5df-66d7-4945-b141-ea87adcfa5d0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_da0f9663-72d0-46a7-9e46-c5380b944eee" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_2c29c5df-66d7-4945-b141-ea87adcfa5d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_d4735aa2-753e-4546-a8da-3b6834f9f338" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_da0f9663-72d0-46a7-9e46-c5380b944eee" xlink:to="loc_us-gaap_ProfitLoss_d4735aa2-753e-4546-a8da-3b6834f9f338" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_13837059-351f-455c-aa28-4d2116075e7a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_da0f9663-72d0-46a7-9e46-c5380b944eee" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_13837059-351f-455c-aa28-4d2116075e7a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_db74d07f-b076-4f2c-9cad-403304bab196" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_da0f9663-72d0-46a7-9e46-c5380b944eee" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_db74d07f-b076-4f2c-9cad-403304bab196" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_a91cc34d-db69-4f3f-b0b5-a610b9bcaf4e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_da0f9663-72d0-46a7-9e46-c5380b944eee" xlink:to="loc_us-gaap_DividendsCommonStockCash_a91cc34d-db69-4f3f-b0b5-a610b9bcaf4e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_422b3b00-e060-414c-adcb-a952abc47bbe" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_da0f9663-72d0-46a7-9e46-c5380b944eee" xlink:to="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_422b3b00-e060-414c-adcb-a952abc47bbe" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_909e5e4e-a493-49a2-b3a8-cf090f6890e7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/RevenueMajorServiceCategoriesDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#RevenueMajorServiceCategoriesDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/RevenueMajorServiceCategoriesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_38dada0a-eff1-4558-a8b4-8de5b37a290b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_52fac6ee-8c1f-42a9-8aea-b284ac6bef4d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_38dada0a-eff1-4558-a8b4-8de5b37a290b" xlink:to="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_52fac6ee-8c1f-42a9-8aea-b284ac6bef4d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_ccb6a619-8ed5-4584-bcb3-99fedb863e3a" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_52fac6ee-8c1f-42a9-8aea-b284ac6bef4d" xlink:to="loc_srt_ProductOrServiceAxis_ccb6a619-8ed5-4584-bcb3-99fedb863e3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_ccb6a619-8ed5-4584-bcb3-99fedb863e3a_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_ccb6a619-8ed5-4584-bcb3-99fedb863e3a" xlink:to="loc_srt_ProductsAndServicesDomain_ccb6a619-8ed5-4584-bcb3-99fedb863e3a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_596d56c0-2c7a-4d90-8310-f55ab5b9da18" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_ccb6a619-8ed5-4584-bcb3-99fedb863e3a" xlink:to="loc_srt_ProductsAndServicesDomain_596d56c0-2c7a-4d90-8310-f55ab5b9da18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_CertificationTestingMember_eabb50db-319e-4a6d-8a03-857c636020aa" xlink:href="uls-20250331.xsd#uls_CertificationTestingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_596d56c0-2c7a-4d90-8310-f55ab5b9da18" xlink:to="loc_uls_CertificationTestingMember_eabb50db-319e-4a6d-8a03-857c636020aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_OngoingCertificationServicesMember_46b73478-e874-469b-9e80-96706a651d01" xlink:href="uls-20250331.xsd#uls_OngoingCertificationServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_596d56c0-2c7a-4d90-8310-f55ab5b9da18" xlink:to="loc_uls_OngoingCertificationServicesMember_46b73478-e874-469b-9e80-96706a651d01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_NonCertificationTestingAndOtherServicesMember_b3d4cc9c-ae17-4b55-a017-1394c851b6d5" xlink:href="uls-20250331.xsd#uls_NonCertificationTestingAndOtherServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_596d56c0-2c7a-4d90-8310-f55ab5b9da18" xlink:to="loc_uls_NonCertificationTestingAndOtherServicesMember_b3d4cc9c-ae17-4b55-a017-1394c851b6d5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_SoftwareMember_0635d965-598a-4128-9350-18e68fdd228d" xlink:href="uls-20250331.xsd#uls_SoftwareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_596d56c0-2c7a-4d90-8310-f55ab5b9da18" xlink:to="loc_uls_SoftwareMember_0635d965-598a-4128-9350-18e68fdd228d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_81b8f30f-2ee1-4540-b390-1ab685bbe01b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_38dada0a-eff1-4558-a8b4-8de5b37a290b" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_81b8f30f-2ee1-4540-b390-1ab685bbe01b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/RevenueNarrativeDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#RevenueNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/RevenueNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_fae048f6-3a96-4271-8543-1521d8a9c011" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_8a258ad2-530b-4e08-9aa0-4dde233715e1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_fae048f6-3a96-4271-8543-1521d8a9c011" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_8a258ad2-530b-4e08-9aa0-4dde233715e1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_3a3f208d-5483-4593-b6b4-bd627b14325b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_8a258ad2-530b-4e08-9aa0-4dde233715e1" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_3a3f208d-5483-4593-b6b4-bd627b14325b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_cf0eec86-757e-4218-8fe0-d52757a8f8dc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_fae048f6-3a96-4271-8543-1521d8a9c011" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_cf0eec86-757e-4218-8fe0-d52757a8f8dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_ae40e6dc-a417-4654-b083-853640397a39" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_fae048f6-3a96-4271-8543-1521d8a9c011" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_ae40e6dc-a417-4654-b083-853640397a39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_9bd68cb0-1328-4760-9c07-faedcc9738d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_fae048f6-3a96-4271-8543-1521d8a9c011" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_9bd68cb0-1328-4760-9c07-faedcc9738d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_477f6542-3533-43bf-82ef-128fb16e4254" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_fae048f6-3a96-4271-8543-1521d8a9c011" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_477f6542-3533-43bf-82ef-128fb16e4254" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/RevenueNarrativeDetails_1" xlink:type="simple" xlink:href="uls-20250331.xsd#RevenueNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/RevenueNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_fae048f6-3a96-4271-8543-1521d8a9c011" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_8a258ad2-530b-4e08-9aa0-4dde233715e1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_fae048f6-3a96-4271-8543-1521d8a9c011" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_8a258ad2-530b-4e08-9aa0-4dde233715e1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_cf0eec86-757e-4218-8fe0-d52757a8f8dc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_fae048f6-3a96-4271-8543-1521d8a9c011" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_cf0eec86-757e-4218-8fe0-d52757a8f8dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_ae40e6dc-a417-4654-b083-853640397a39" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_fae048f6-3a96-4271-8543-1521d8a9c011" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_ae40e6dc-a417-4654-b083-853640397a39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_9bd68cb0-1328-4760-9c07-faedcc9738d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_fae048f6-3a96-4271-8543-1521d8a9c011" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_9bd68cb0-1328-4760-9c07-faedcc9738d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_477f6542-3533-43bf-82ef-128fb16e4254" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_fae048f6-3a96-4271-8543-1521d8a9c011" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_477f6542-3533-43bf-82ef-128fb16e4254" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/AcquisitionsandDivestituresAcquisitionsDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#AcquisitionsandDivestituresAcquisitionsDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/AcquisitionsandDivestituresAcquisitionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_aa377a90-8a24-475c-afb7-883aa8be2366" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_7cf40082-eb04-42a9-b8b6-ce10d5a57124" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_aa377a90-8a24-475c-afb7-883aa8be2366" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_7cf40082-eb04-42a9-b8b6-ce10d5a57124" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_d884aa7c-0e83-43a2-9796-cc10431cc2e9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_7cf40082-eb04-42a9-b8b6-ce10d5a57124" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_d884aa7c-0e83-43a2-9796-cc10431cc2e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d884aa7c-0e83-43a2-9796-cc10431cc2e9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_d884aa7c-0e83-43a2-9796-cc10431cc2e9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d884aa7c-0e83-43a2-9796-cc10431cc2e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8084104c-49a5-4152-8980-4ccfd5477a05" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_d884aa7c-0e83-43a2-9796-cc10431cc2e9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8084104c-49a5-4152-8980-4ccfd5477a05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_TesTneTEngineeringGmbHMember_ec89eae5-3e49-451d-99e9-40ce7e39ddcc" xlink:href="uls-20250331.xsd#uls_TesTneTEngineeringGmbHMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8084104c-49a5-4152-8980-4ccfd5477a05" xlink:to="loc_uls_TesTneTEngineeringGmbHMember_ec89eae5-3e49-451d-99e9-40ce7e39ddcc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_BatterielngenieureGmbHBatterielngenieureMember_bee432d3-9b50-4433-a3eb-59c9a0d4b4da" xlink:href="uls-20250331.xsd#uls_BatterielngenieureGmbHBatterielngenieureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8084104c-49a5-4152-8980-4ccfd5477a05" xlink:to="loc_uls_BatterielngenieureGmbHBatterielngenieureMember_bee432d3-9b50-4433-a3eb-59c9a0d4b4da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_0761a989-9038-4838-93ad-b62d7f4c16e2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_aa377a90-8a24-475c-afb7-883aa8be2366" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_0761a989-9038-4838-93ad-b62d7f4c16e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_e25d83d5-c010-42ce-b370-56135b22b4f0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_aa377a90-8a24-475c-afb7-883aa8be2366" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_e25d83d5-c010-42ce-b370-56135b22b4f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_5605fa62-ed63-4d88-acf8-ab59d45755fa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_aa377a90-8a24-475c-afb7-883aa8be2366" xlink:to="loc_us-gaap_Goodwill_5605fa62-ed63-4d88-acf8-ab59d45755fa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_d5fa17e4-051a-48a5-82b0-e4feb111787b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_aa377a90-8a24-475c-afb7-883aa8be2366" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_d5fa17e4-051a-48a5-82b0-e4feb111787b" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/AcquisitionsandDivestituresDivestituresandHeldforSaleDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#AcquisitionsandDivestituresDivestituresandHeldforSaleDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/AcquisitionsandDivestituresDivestituresandHeldforSaleDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_579f1504-ff86-4795-bdba-760e6707e3d9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_4aa2cb22-01a6-4200-a2f6-03eda639c450" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_579f1504-ff86-4795-bdba-760e6707e3d9" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_4aa2cb22-01a6-4200-a2f6-03eda639c450" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_dcf5628a-74de-47be-95cb-330b1e4b38ff" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_4aa2cb22-01a6-4200-a2f6-03eda639c450" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_dcf5628a-74de-47be-95cb-330b1e4b38ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_dcf5628a-74de-47be-95cb-330b1e4b38ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_dcf5628a-74de-47be-95cb-330b1e4b38ff" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_dcf5628a-74de-47be-95cb-330b1e4b38ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_4c04b23f-4e15-4bcf-b56a-5f1221d76159" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_dcf5628a-74de-47be-95cb-330b1e4b38ff" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_4c04b23f-4e15-4bcf-b56a-5f1221d76159" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_9c5c680c-204c-4811-9889-d1919599a7a4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_4c04b23f-4e15-4bcf-b56a-5f1221d76159" xlink:to="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_9c5c680c-204c-4811-9889-d1919599a7a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_38765dd5-1914-48c8-9f87-ba0d905ddb1a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_4aa2cb22-01a6-4200-a2f6-03eda639c450" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_38765dd5-1914-48c8-9f87-ba0d905ddb1a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_38765dd5-1914-48c8-9f87-ba0d905ddb1a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_38765dd5-1914-48c8-9f87-ba0d905ddb1a" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_38765dd5-1914-48c8-9f87-ba0d905ddb1a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_7e312963-3de2-4d21-ae0f-96c45a59dbf5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_38765dd5-1914-48c8-9f87-ba0d905ddb1a" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_7e312963-3de2-4d21-ae0f-96c45a59dbf5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_PaymentsTestingBusinessMember_4498091d-c9d2-4e2d-83e5-5133418a21b8" xlink:href="uls-20250331.xsd#uls_PaymentsTestingBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_7e312963-3de2-4d21-ae0f-96c45a59dbf5" xlink:to="loc_uls_PaymentsTestingBusinessMember_4498091d-c9d2-4e2d-83e5-5133418a21b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_0b3f8d22-b97d-482e-9453-9865058034de" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_579f1504-ff86-4795-bdba-760e6707e3d9" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_0b3f8d22-b97d-482e-9453-9865058034de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_4b895cfc-ffc8-48b2-ba69-81e48bfa5269" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_579f1504-ff86-4795-bdba-760e6707e3d9" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_4b895cfc-ffc8-48b2-ba69-81e48bfa5269" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/FairValueofFinancialInstrumentsDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#FairValueofFinancialInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/FairValueofFinancialInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_02ecc6e5-2177-46b6-b25a-ea32c3e959ee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_bc312209-d755-43a4-97c5-1b0f0d193454" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_02ecc6e5-2177-46b6-b25a-ea32c3e959ee" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_bc312209-d755-43a4-97c5-1b0f0d193454" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_b0d25393-eef3-49a0-83ad-f73d90ea5c27" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_bc312209-d755-43a4-97c5-1b0f0d193454" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_b0d25393-eef3-49a0-83ad-f73d90ea5c27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_b0d25393-eef3-49a0-83ad-f73d90ea5c27_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_b0d25393-eef3-49a0-83ad-f73d90ea5c27" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_b0d25393-eef3-49a0-83ad-f73d90ea5c27_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_a0493567-278e-4b40-aafc-3dcabcbfb33b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_b0d25393-eef3-49a0-83ad-f73d90ea5c27" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_a0493567-278e-4b40-aafc-3dcabcbfb33b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_330e4ce1-d7de-4b30-b187-dcc414546529" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_a0493567-278e-4b40-aafc-3dcabcbfb33b" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_330e4ce1-d7de-4b30-b187-dcc414546529" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_b6960d2b-2868-4b2f-8651-bffbea67c572" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_330e4ce1-d7de-4b30-b187-dcc414546529" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_b6960d2b-2868-4b2f-8651-bffbea67c572" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_247e9746-2a6e-4b2b-83ff-c2ef6adf1167" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_330e4ce1-d7de-4b30-b187-dcc414546529" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_247e9746-2a6e-4b2b-83ff-c2ef6adf1167" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_90d50241-abd9-4204-80c4-73e600df3cf6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_bc312209-d755-43a4-97c5-1b0f0d193454" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_90d50241-abd9-4204-80c4-73e600df3cf6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_90d50241-abd9-4204-80c4-73e600df3cf6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_90d50241-abd9-4204-80c4-73e600df3cf6" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_90d50241-abd9-4204-80c4-73e600df3cf6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_3439f2bc-57f1-4605-a21f-ebb5ad29743b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_90d50241-abd9-4204-80c4-73e600df3cf6" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_3439f2bc-57f1-4605-a21f-ebb5ad29743b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_e97175b5-30cf-47d8-a3de-1b7e927d195a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_3439f2bc-57f1-4605-a21f-ebb5ad29743b" xlink:to="loc_us-gaap_UnsecuredDebtMember_e97175b5-30cf-47d8-a3de-1b7e927d195a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_5fbbbe28-7fec-4df9-8f81-181d85b684b4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_3439f2bc-57f1-4605-a21f-ebb5ad29743b" xlink:to="loc_us-gaap_SeniorNotesMember_5fbbbe28-7fec-4df9-8f81-181d85b684b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_OtherMember_c95f54f2-363b-47d0-a334-e852c9c1cbcd" xlink:href="uls-20250331.xsd#uls_OtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_3439f2bc-57f1-4605-a21f-ebb5ad29743b" xlink:to="loc_uls_OtherMember_c95f54f2-363b-47d0-a334-e852c9c1cbcd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_50b9d5c2-f2c3-41ea-acb9-d2dea01c0f5f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_02ecc6e5-2177-46b6-b25a-ea32c3e959ee" xlink:to="loc_us-gaap_LongTermDebtFairValue_50b9d5c2-f2c3-41ea-acb9-d2dea01c0f5f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/InvestmentsinEquitySecuritiesDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#InvestmentsinEquitySecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/InvestmentsinEquitySecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_fe099c15-74b4-45be-bb2e-40a989c74927" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_89876bf0-c5fa-45e2-9dfc-a593cc89191d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_fe099c15-74b4-45be-bb2e-40a989c74927" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_89876bf0-c5fa-45e2-9dfc-a593cc89191d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_80263924-b9cc-4866-9dab-592f8eded1dc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_89876bf0-c5fa-45e2-9dfc-a593cc89191d" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_80263924-b9cc-4866-9dab-592f8eded1dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_80263924-b9cc-4866-9dab-592f8eded1dc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_80263924-b9cc-4866-9dab-592f8eded1dc" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_80263924-b9cc-4866-9dab-592f8eded1dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_6b54850d-3f8a-4f3b-b2a7-230d779a7dfa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_80263924-b9cc-4866-9dab-592f8eded1dc" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_6b54850d-3f8a-4f3b-b2a7-230d779a7dfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_ULCCICCompanyLimitedMember_7a757876-8379-4191-8b29-a206d3a93b46" xlink:href="uls-20250331.xsd#uls_ULCCICCompanyLimitedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_6b54850d-3f8a-4f3b-b2a7-230d779a7dfa" xlink:to="loc_uls_ULCCICCompanyLimitedMember_7a757876-8379-4191-8b29-a206d3a93b46" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_d39158ad-48e3-4e8c-9114-289f6672bdb9" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_89876bf0-c5fa-45e2-9dfc-a593cc89191d" xlink:to="loc_srt_ConsolidatedEntitiesAxis_d39158ad-48e3-4e8c-9114-289f6672bdb9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_d39158ad-48e3-4e8c-9114-289f6672bdb9_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_d39158ad-48e3-4e8c-9114-289f6672bdb9" xlink:to="loc_srt_ConsolidatedEntitiesDomain_d39158ad-48e3-4e8c-9114-289f6672bdb9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_e9842cee-1bea-4de5-8f68-94d4253f85a9" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_d39158ad-48e3-4e8c-9114-289f6672bdb9" xlink:to="loc_srt_ConsolidatedEntitiesDomain_e9842cee-1bea-4de5-8f68-94d4253f85a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_021acd21-41c3-4891-a2ff-f3a55b0e4e64" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_e9842cee-1bea-4de5-8f68-94d4253f85a9" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_021acd21-41c3-4891-a2ff-f3a55b0e4e64" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_c6642b4e-5a3a-44d4-9017-ac093a486a73" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_fe099c15-74b4-45be-bb2e-40a989c74927" xlink:to="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_c6642b4e-5a3a-44d4-9017-ac093a486a73" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityOwnershipPercentage_f891e42b-63c7-455e-b7ca-beef11481d53" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableInterestEntityOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_fe099c15-74b4-45be-bb2e-40a989c74927" xlink:to="loc_us-gaap_VariableInterestEntityOwnershipPercentage_f891e42b-63c7-455e-b7ca-beef11481d53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_d8e962fa-e018-44fa-84a4-0ad9a6ffb0c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_fe099c15-74b4-45be-bb2e-40a989c74927" xlink:to="loc_us-gaap_Assets_d8e962fa-e018-44fa-84a4-0ad9a6ffb0c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_bd7490d7-dfdd-4237-aa1f-1bf8facf779e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_fe099c15-74b4-45be-bb2e-40a989c74927" xlink:to="loc_us-gaap_Liabilities_bd7490d7-dfdd-4237-aa1f-1bf8facf779e" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/GoodwillDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#GoodwillDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/GoodwillDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_ab5d4a5a-c894-48d6-9f2c-cde52fb3016e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_386ec8cd-e743-4521-b907-47c9352a2258" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_ab5d4a5a-c894-48d6-9f2c-cde52fb3016e" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_386ec8cd-e743-4521-b907-47c9352a2258" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_04c04178-feed-4f61-91e8-810e94856cd8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_386ec8cd-e743-4521-b907-47c9352a2258" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_04c04178-feed-4f61-91e8-810e94856cd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_04c04178-feed-4f61-91e8-810e94856cd8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_04c04178-feed-4f61-91e8-810e94856cd8" xlink:to="loc_us-gaap_SegmentDomain_04c04178-feed-4f61-91e8-810e94856cd8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_0ca6b21b-e6f3-42f8-a99a-cf6907c68175" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_04c04178-feed-4f61-91e8-810e94856cd8" xlink:to="loc_us-gaap_SegmentDomain_0ca6b21b-e6f3-42f8-a99a-cf6907c68175" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_IndustrialMember_78ca7c9f-883f-4575-bd6a-5300fdda43d5" xlink:href="uls-20250331.xsd#uls_IndustrialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_0ca6b21b-e6f3-42f8-a99a-cf6907c68175" xlink:to="loc_uls_IndustrialMember_78ca7c9f-883f-4575-bd6a-5300fdda43d5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_ConsumerMember_baad22e0-acd3-4b42-95b2-a8cc765a633b" xlink:href="uls-20250331.xsd#uls_ConsumerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_0ca6b21b-e6f3-42f8-a99a-cf6907c68175" xlink:to="loc_uls_ConsumerMember_baad22e0-acd3-4b42-95b2-a8cc765a633b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_SoftwareAndAdvisoryMember_7a55d6d3-61b8-42f6-8c62-665e29ba82f8" xlink:href="uls-20250331.xsd#uls_SoftwareAndAdvisoryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_0ca6b21b-e6f3-42f8-a99a-cf6907c68175" xlink:to="loc_uls_SoftwareAndAdvisoryMember_7a55d6d3-61b8-42f6-8c62-665e29ba82f8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_48646d6a-8d66-46ad-bc26-d78a9999d574" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_386ec8cd-e743-4521-b907-47c9352a2258" xlink:to="loc_srt_ConsolidationItemsAxis_48646d6a-8d66-46ad-bc26-d78a9999d574" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_48646d6a-8d66-46ad-bc26-d78a9999d574_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_48646d6a-8d66-46ad-bc26-d78a9999d574" xlink:to="loc_srt_ConsolidationItemsDomain_48646d6a-8d66-46ad-bc26-d78a9999d574_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_212736a7-65c3-4b69-bf3a-879480cc4a6f" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_48646d6a-8d66-46ad-bc26-d78a9999d574" xlink:to="loc_srt_ConsolidationItemsDomain_212736a7-65c3-4b69-bf3a-879480cc4a6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_4208ddb5-cf8b-490d-aafc-d8b44f5e1ee2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_212736a7-65c3-4b69-bf3a-879480cc4a6f" xlink:to="loc_us-gaap_OperatingSegmentsMember_4208ddb5-cf8b-490d-aafc-d8b44f5e1ee2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillRollForward_9e23acdf-e2b0-42c4-91c6-d76e7698609d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_ab5d4a5a-c894-48d6-9f2c-cde52fb3016e" xlink:to="loc_us-gaap_GoodwillRollForward_9e23acdf-e2b0-42c4-91c6-d76e7698609d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_b4c1b369-0163-4278-ad5b-fc1344d34dc3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_9e23acdf-e2b0-42c4-91c6-d76e7698609d" xlink:to="loc_us-gaap_Goodwill_b4c1b369-0163-4278-ad5b-fc1344d34dc3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_d9cfa68e-67a5-43f5-9a51-b817b58951c7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_9e23acdf-e2b0-42c4-91c6-d76e7698609d" xlink:to="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_d9cfa68e-67a5-43f5-9a51-b817b58951c7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_73b404f7-cd84-4c24-94f5-3e3ad806dbdf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillForeignCurrencyTranslationGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_9e23acdf-e2b0-42c4-91c6-d76e7698609d" xlink:to="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_73b404f7-cd84-4c24-94f5-3e3ad806dbdf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_1b85977f-4283-4976-b855-108a6dc2b123" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_e5487d47-4e29-41b4-b2b8-b04f9fec48ad" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillImpairedAccumulatedImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_ab5d4a5a-c894-48d6-9f2c-cde52fb3016e" xlink:to="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_e5487d47-4e29-41b4-b2b8-b04f9fec48ad" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/IntangibleAssetsDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#IntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/IntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_7f0989ec-7eae-40b2-bfec-ca15d49da748" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_ddc90d01-f596-42a4-b195-bb8c077d6e52" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_7f0989ec-7eae-40b2-bfec-ca15d49da748" xlink:to="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_ddc90d01-f596-42a4-b195-bb8c077d6e52" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_2319b77d-0311-41f4-82a3-5df099492fad" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_ddc90d01-f596-42a4-b195-bb8c077d6e52" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_2319b77d-0311-41f4-82a3-5df099492fad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2319b77d-0311-41f4-82a3-5df099492fad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_2319b77d-0311-41f4-82a3-5df099492fad" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2319b77d-0311-41f4-82a3-5df099492fad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_93638dba-e319-46e0-baf4-71b7813b47c8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_2319b77d-0311-41f4-82a3-5df099492fad" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_93638dba-e319-46e0-baf4-71b7813b47c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_46e3b6a6-fda0-443c-a5ee-178e6184d8e4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_93638dba-e319-46e0-baf4-71b7813b47c8" xlink:to="loc_us-gaap_CustomerRelationshipsMember_46e3b6a6-fda0-443c-a5ee-178e6184d8e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_IntellectualPropertyAndPatentsMember_8ebd3720-78d3-4401-bf88-a9a54cf75f2e" xlink:href="uls-20250331.xsd#uls_IntellectualPropertyAndPatentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_93638dba-e319-46e0-baf4-71b7813b47c8" xlink:to="loc_uls_IntellectualPropertyAndPatentsMember_8ebd3720-78d3-4401-bf88-a9a54cf75f2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksMember_b44a716c-3200-448e-9223-985f9f254752" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TrademarksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_93638dba-e319-46e0-baf4-71b7813b47c8" xlink:to="loc_us-gaap_TrademarksMember_b44a716c-3200-448e-9223-985f9f254752" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_0c1b081a-4ab1-41cd-8059-64312edf8137" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_7f0989ec-7eae-40b2-bfec-ca15d49da748" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_0c1b081a-4ab1-41cd-8059-64312edf8137" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_09df50af-d108-4937-874d-8325a0f5cd86" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_7f0989ec-7eae-40b2-bfec-ca15d49da748" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_09df50af-d108-4937-874d-8325a0f5cd86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_0f1ccd9b-1583-4615-8239-3ab27f9ad37d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_7f0989ec-7eae-40b2-bfec-ca15d49da748" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_0f1ccd9b-1583-4615-8239-3ab27f9ad37d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_1e02dfc6-28a3-45b1-9ac5-046aff58d615" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_7f0989ec-7eae-40b2-bfec-ca15d49da748" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_1e02dfc6-28a3-45b1-9ac5-046aff58d615" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/LongTermDebtOutstandingDebtDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#LongTermDebtOutstandingDebtDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/LongTermDebtOutstandingDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_f6748cf0-dab5-453b-a50a-98a74c7235c3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_2c342184-0925-4c0a-862c-0f9a0daff6cf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f6748cf0-dab5-453b-a50a-98a74c7235c3" xlink:to="loc_us-gaap_DebtInstrumentTable_2c342184-0925-4c0a-862c-0f9a0daff6cf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_97a4d724-6b4f-4290-a35c-6e2fdf6b1777" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_2c342184-0925-4c0a-862c-0f9a0daff6cf" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_97a4d724-6b4f-4290-a35c-6e2fdf6b1777" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_97a4d724-6b4f-4290-a35c-6e2fdf6b1777_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_97a4d724-6b4f-4290-a35c-6e2fdf6b1777" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_97a4d724-6b4f-4290-a35c-6e2fdf6b1777_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_c7ed0b28-f059-4f9c-897b-6e5d6a3bce2d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_97a4d724-6b4f-4290-a35c-6e2fdf6b1777" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_c7ed0b28-f059-4f9c-897b-6e5d6a3bce2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_5481073d-382d-4863-bec9-445dd0856c15" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_c7ed0b28-f059-4f9c-897b-6e5d6a3bce2d" xlink:to="loc_us-gaap_UnsecuredDebtMember_5481073d-382d-4863-bec9-445dd0856c15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_fdca8d06-40ff-4e76-a75e-9c0542a9cd17" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_c7ed0b28-f059-4f9c-897b-6e5d6a3bce2d" xlink:to="loc_us-gaap_SeniorNotesMember_fdca8d06-40ff-4e76-a75e-9c0542a9cd17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_OtherMember_80aef1cf-01eb-4f3d-aefc-a001d2d22fc2" xlink:href="uls-20250331.xsd#uls_OtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_c7ed0b28-f059-4f9c-897b-6e5d6a3bce2d" xlink:to="loc_uls_OtherMember_80aef1cf-01eb-4f3d-aefc-a001d2d22fc2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_12fb7e9d-7201-47db-b587-e77f682151a8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f6748cf0-dab5-453b-a50a-98a74c7235c3" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_12fb7e9d-7201-47db-b587-e77f682151a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_4d9bb130-c936-4180-bece-921819e4bbc8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f6748cf0-dab5-453b-a50a-98a74c7235c3" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_4d9bb130-c936-4180-bece-921819e4bbc8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_5d5bae64-1db1-480c-8e87-2b815fedc3ca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f6748cf0-dab5-453b-a50a-98a74c7235c3" xlink:to="loc_us-gaap_LongTermDebt_5d5bae64-1db1-480c-8e87-2b815fedc3ca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_7a7bf276-88f9-4aa4-b60c-df32bc2818b8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f6748cf0-dab5-453b-a50a-98a74c7235c3" xlink:to="loc_us-gaap_LongTermDebtCurrent_7a7bf276-88f9-4aa4-b60c-df32bc2818b8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_1af3f3f7-837f-4951-aa59-cebe013cdd09" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f6748cf0-dab5-453b-a50a-98a74c7235c3" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_1af3f3f7-837f-4951-aa59-cebe013cdd09" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/LongTermDebtNarrativeDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#LongTermDebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/LongTermDebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_0966d73e-2710-45c8-b486-79e233fa3ac2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_351b2782-fe90-465b-841a-a3e9c5181bca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0966d73e-2710-45c8-b486-79e233fa3ac2" xlink:to="loc_us-gaap_DebtInstrumentTable_351b2782-fe90-465b-841a-a3e9c5181bca" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_12913305-e701-41b5-8a9d-f69608f1f10b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_351b2782-fe90-465b-841a-a3e9c5181bca" xlink:to="loc_us-gaap_DebtInstrumentAxis_12913305-e701-41b5-8a9d-f69608f1f10b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_12913305-e701-41b5-8a9d-f69608f1f10b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_12913305-e701-41b5-8a9d-f69608f1f10b" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_12913305-e701-41b5-8a9d-f69608f1f10b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_2e884ad3-2b69-40fe-9a71-002baacf718f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_12913305-e701-41b5-8a9d-f69608f1f10b" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_2e884ad3-2b69-40fe-9a71-002baacf718f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_CreditFacilityMember_5e6afe29-570a-4aa3-b9a4-373686ee50bf" xlink:href="uls-20250331.xsd#uls_CreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_2e884ad3-2b69-40fe-9a71-002baacf718f" xlink:to="loc_uls_CreditFacilityMember_5e6afe29-570a-4aa3-b9a4-373686ee50bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_SeniorNotesDue2028Member_a2a76807-de4f-400f-a94a-c41af8e6938c" xlink:href="uls-20250331.xsd#uls_SeniorNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_2e884ad3-2b69-40fe-9a71-002baacf718f" xlink:to="loc_uls_SeniorNotesDue2028Member_a2a76807-de4f-400f-a94a-c41af8e6938c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_b66fa08c-4b4f-4406-a169-489281572b82" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_351b2782-fe90-465b-841a-a3e9c5181bca" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_b66fa08c-4b4f-4406-a169-489281572b82" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_b66fa08c-4b4f-4406-a169-489281572b82_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_b66fa08c-4b4f-4406-a169-489281572b82" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_b66fa08c-4b4f-4406-a169-489281572b82_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_5ce257c8-3e08-482b-b7d6-37f6fe08dda0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_b66fa08c-4b4f-4406-a169-489281572b82" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_5ce257c8-3e08-482b-b7d6-37f6fe08dda0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_1457c613-c094-491e-996f-cf02df8a7146" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_5ce257c8-3e08-482b-b7d6-37f6fe08dda0" xlink:to="loc_us-gaap_UnsecuredDebtMember_1457c613-c094-491e-996f-cf02df8a7146" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_17e1050f-f424-4299-8464-5f79f57e54c4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_5ce257c8-3e08-482b-b7d6-37f6fe08dda0" xlink:to="loc_us-gaap_SeniorNotesMember_17e1050f-f424-4299-8464-5f79f57e54c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_ff4a5d04-5b6e-4794-b0be-dabe65e193bf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_351b2782-fe90-465b-841a-a3e9c5181bca" xlink:to="loc_us-gaap_CreditFacilityAxis_ff4a5d04-5b6e-4794-b0be-dabe65e193bf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_ff4a5d04-5b6e-4794-b0be-dabe65e193bf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_ff4a5d04-5b6e-4794-b0be-dabe65e193bf" xlink:to="loc_us-gaap_CreditFacilityDomain_ff4a5d04-5b6e-4794-b0be-dabe65e193bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_e0e78872-18e6-4fb8-acd1-1ad920e8a557" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_ff4a5d04-5b6e-4794-b0be-dabe65e193bf" xlink:to="loc_us-gaap_CreditFacilityDomain_e0e78872-18e6-4fb8-acd1-1ad920e8a557" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_TermLoansAndRevolvingCreditFacilityMember_088f5c3b-a810-484e-b365-b0f677d7b315" xlink:href="uls-20250331.xsd#uls_TermLoansAndRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_e0e78872-18e6-4fb8-acd1-1ad920e8a557" xlink:to="loc_uls_TermLoansAndRevolvingCreditFacilityMember_088f5c3b-a810-484e-b365-b0f677d7b315" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_bdf9d6bd-bfd3-4978-866b-e66728c32d11" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0966d73e-2710-45c8-b486-79e233fa3ac2" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_bdf9d6bd-bfd3-4978-866b-e66728c32d11" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtWeightedAverageInterestRate_d5453666-3ca6-4875-90ed-86945d0c69cb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtWeightedAverageInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0966d73e-2710-45c8-b486-79e233fa3ac2" xlink:to="loc_us-gaap_DebtWeightedAverageInterestRate_d5453666-3ca6-4875-90ed-86945d0c69cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_edee3ec3-844d-416c-945b-222062c15425" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0966d73e-2710-45c8-b486-79e233fa3ac2" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_edee3ec3-844d-416c-945b-222062c15425" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_f7da4a07-1e68-4826-8a50-835e5e3cf342" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0966d73e-2710-45c8-b486-79e233fa3ac2" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_f7da4a07-1e68-4826-8a50-835e5e3cf342" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/AccumulatedOtherComprehensiveLossDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#AccumulatedOtherComprehensiveLossDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/AccumulatedOtherComprehensiveLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_bb8f353d-041d-401a-96b0-f1d214fd83c8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_56814710-ba1c-48eb-841b-5cbba61f5747" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_bb8f353d-041d-401a-96b0-f1d214fd83c8" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_56814710-ba1c-48eb-841b-5cbba61f5747" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_40977420-c55d-4379-b82c-63f46d295d76" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_56814710-ba1c-48eb-841b-5cbba61f5747" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_40977420-c55d-4379-b82c-63f46d295d76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_40977420-c55d-4379-b82c-63f46d295d76_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_40977420-c55d-4379-b82c-63f46d295d76" xlink:to="loc_us-gaap_EquityComponentDomain_40977420-c55d-4379-b82c-63f46d295d76_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_6469b6a0-bf95-4c18-ad2c-27f729072019" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_40977420-c55d-4379-b82c-63f46d295d76" xlink:to="loc_us-gaap_EquityComponentDomain_6469b6a0-bf95-4c18-ad2c-27f729072019" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_d7d3d03e-a327-40a0-9932-e84a6335d1df" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_6469b6a0-bf95-4c18-ad2c-27f729072019" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_d7d3d03e-a327-40a0-9932-e84a6335d1df" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_99db5f30-500a-4c0f-9b28-4261497c9a1f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_6469b6a0-bf95-4c18-ad2c-27f729072019" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_99db5f30-500a-4c0f-9b28-4261497c9a1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_1975046f-ee09-4719-b99a-688f836a283e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_6469b6a0-bf95-4c18-ad2c-27f729072019" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_1975046f-ee09-4719-b99a-688f836a283e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_82caf1bf-1b1e-4e95-b679-8bb17d76aecd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_bb8f353d-041d-401a-96b0-f1d214fd83c8" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_82caf1bf-1b1e-4e95-b679-8bb17d76aecd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_a22564d6-fb8d-4f2b-84e7-485002cd8287" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_82caf1bf-1b1e-4e95-b679-8bb17d76aecd" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_a22564d6-fb8d-4f2b-84e7-485002cd8287" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_ca1d2110-2dd6-43e3-b822-73e8a15e7086" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_82caf1bf-1b1e-4e95-b679-8bb17d76aecd" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_ca1d2110-2dd6-43e3-b822-73e8a15e7086" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_622cfc57-25ce-47d9-91b9-d728c7c55435" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_82caf1bf-1b1e-4e95-b679-8bb17d76aecd" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_622cfc57-25ce-47d9-91b9-d728c7c55435" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_88dc1686-beee-4968-8ee5-a272fc9f4952" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_82caf1bf-1b1e-4e95-b679-8bb17d76aecd" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_88dc1686-beee-4968-8ee5-a272fc9f4952" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_afd08450-bec2-4dad-ac19-075a637b6232" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/StockbasedandOtherIncentiveCompensationCompensationExpenseDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#StockbasedandOtherIncentiveCompensationCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/StockbasedandOtherIncentiveCompensationCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_815a9e19-0145-4347-a217-8f518eff7ad5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_b4a2d02f-a523-461a-8ed9-e069f4354f49" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_815a9e19-0145-4347-a217-8f518eff7ad5" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_b4a2d02f-a523-461a-8ed9-e069f4354f49" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_1cc4736f-6e37-462b-b13f-5695e488f0c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_b4a2d02f-a523-461a-8ed9-e069f4354f49" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_1cc4736f-6e37-462b-b13f-5695e488f0c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_1cc4736f-6e37-462b-b13f-5695e488f0c5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_1cc4736f-6e37-462b-b13f-5695e488f0c5" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_1cc4736f-6e37-462b-b13f-5695e488f0c5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_8f4f18bc-432b-4ecf-8cc9-0060129fab61" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_1cc4736f-6e37-462b-b13f-5695e488f0c5" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_8f4f18bc-432b-4ecf-8cc9-0060129fab61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_67c4fea7-a549-449f-b13d-e9aad2919dfd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_8f4f18bc-432b-4ecf-8cc9-0060129fab61" xlink:to="loc_us-gaap_CostOfSalesMember_67c4fea7-a549-449f-b13d-e9aad2919dfd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_f8751139-a69a-4e93-a94e-6b4c30e86675" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_8f4f18bc-432b-4ecf-8cc9-0060129fab61" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_f8751139-a69a-4e93-a94e-6b4c30e86675" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_ac6c0ae8-0a37-44df-b4b0-2936948ff17d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_b4a2d02f-a523-461a-8ed9-e069f4354f49" xlink:to="loc_us-gaap_AwardTypeAxis_ac6c0ae8-0a37-44df-b4b0-2936948ff17d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ac6c0ae8-0a37-44df-b4b0-2936948ff17d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_ac6c0ae8-0a37-44df-b4b0-2936948ff17d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ac6c0ae8-0a37-44df-b4b0-2936948ff17d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_13cea20c-b03b-4889-835d-d73f7f0aa39f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_ac6c0ae8-0a37-44df-b4b0-2936948ff17d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_13cea20c-b03b-4889-835d-d73f7f0aa39f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_7d797d74-2f1f-4cdf-b040-82d038e2bf0d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_13cea20c-b03b-4889-835d-d73f7f0aa39f" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_7d797d74-2f1f-4cdf-b040-82d038e2bf0d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_6bee3ee0-a657-447e-aa37-d935a5a6e3ad" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_13cea20c-b03b-4889-835d-d73f7f0aa39f" xlink:to="loc_us-gaap_PerformanceSharesMember_6bee3ee0-a657-447e-aa37-d935a5a6e3ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_32eecae2-d77f-480d-bc5c-000212eeac1a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_13cea20c-b03b-4889-835d-d73f7f0aa39f" xlink:to="loc_us-gaap_EmployeeStockOptionMember_32eecae2-d77f-480d-bc5c-000212eeac1a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_97365e61-eb96-4d7d-8285-6335d9e90887" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_13cea20c-b03b-4889-835d-d73f7f0aa39f" xlink:to="loc_us-gaap_EmployeeStockMember_97365e61-eb96-4d7d-8285-6335d9e90887" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_CashSettledStockAppreciationRightsCSARsMember_359bf8b6-bf2d-4917-a570-07594d455ca8" xlink:href="uls-20250331.xsd#uls_CashSettledStockAppreciationRightsCSARsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_13cea20c-b03b-4889-835d-d73f7f0aa39f" xlink:to="loc_uls_CashSettledStockAppreciationRightsCSARsMember_359bf8b6-bf2d-4917-a570-07594d455ca8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_d72fbba0-a807-440d-8e34-4b47d993dfc4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_815a9e19-0145-4347-a217-8f518eff7ad5" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_d72fbba0-a807-440d-8e34-4b47d993dfc4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_392d1cbf-800c-459a-ac56-16d290bc54ee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_815a9e19-0145-4347-a217-8f518eff7ad5" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_392d1cbf-800c-459a-ac56-16d290bc54ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax_e18e38cb-de6d-4249-a560-134035c174d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_815a9e19-0145-4347-a217-8f518eff7ad5" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax_e18e38cb-de6d-4249-a560-134035c174d6" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/RelatedPartyTransactionsDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#RelatedPartyTransactionsDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/RelatedPartyTransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_4885a8c6-1a41-41cd-8435-224f105ef107" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_f7a57391-e146-4dcc-bba8-b9caf6687f30" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_4885a8c6-1a41-41cd-8435-224f105ef107" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_f7a57391-e146-4dcc-bba8-b9caf6687f30" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_581ee20b-f4c6-4136-833e-af6664d1bf72" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_f7a57391-e146-4dcc-bba8-b9caf6687f30" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_581ee20b-f4c6-4136-833e-af6664d1bf72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_581ee20b-f4c6-4136-833e-af6664d1bf72_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_581ee20b-f4c6-4136-833e-af6664d1bf72" xlink:to="loc_us-gaap_RelatedPartyDomain_581ee20b-f4c6-4136-833e-af6664d1bf72_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_2a541de4-c239-4f2b-bcf8-f799dba39711" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_581ee20b-f4c6-4136-833e-af6664d1bf72" xlink:to="loc_us-gaap_RelatedPartyDomain_2a541de4-c239-4f2b-bcf8-f799dba39711" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_33f8ae64-a5cf-4ca2-8151-13241b2b5436" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_2a541de4-c239-4f2b-bcf8-f799dba39711" xlink:to="loc_us-gaap_RelatedPartyMember_33f8ae64-a5cf-4ca2-8151-13241b2b5436" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_0f7c1fe0-79ca-4b68-bf87-4ec0c63040d7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_f7a57391-e146-4dcc-bba8-b9caf6687f30" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_0f7c1fe0-79ca-4b68-bf87-4ec0c63040d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_0f7c1fe0-79ca-4b68-bf87-4ec0c63040d7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_0f7c1fe0-79ca-4b68-bf87-4ec0c63040d7" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_0f7c1fe0-79ca-4b68-bf87-4ec0c63040d7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_574f0c11-55c6-440b-be9a-0ed983f43678" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_0f7c1fe0-79ca-4b68-bf87-4ec0c63040d7" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_574f0c11-55c6-440b-be9a-0ed983f43678" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_ULStandardsEngagementTransactionsMember_b2337cc1-4b0d-4f86-b77d-9be5ceb125f5" xlink:href="uls-20250331.xsd#uls_ULStandardsEngagementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_574f0c11-55c6-440b-be9a-0ed983f43678" xlink:to="loc_uls_ULStandardsEngagementTransactionsMember_b2337cc1-4b0d-4f86-b77d-9be5ceb125f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_fe0c009c-e889-437a-a60a-99cdaade4dd1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionAmountsOfTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_4885a8c6-1a41-41cd-8435-224f105ef107" xlink:to="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_fe0c009c-e889-437a-a60a-99cdaade4dd1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_683d2322-14d8-43dd-9630-912e63e1f639" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_4885a8c6-1a41-41cd-8435-224f105ef107" xlink:to="loc_us-gaap_DividendsCommonStockCash_683d2322-14d8-43dd-9630-912e63e1f639" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ul.com/role/SegmentInformationScheduleOfSegmentExpensesAndOperatingIncomeDetails" xlink:type="simple" xlink:href="uls-20250331.xsd#SegmentInformationScheduleOfSegmentExpensesAndOperatingIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.ul.com/role/SegmentInformationScheduleOfSegmentExpensesAndOperatingIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_3cfd2073-1165-4018-8a98-483a7ca9f99d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_e7a380a9-9e2c-4704-8b8c-0cfc062d0acf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3cfd2073-1165-4018-8a98-483a7ca9f99d" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_e7a380a9-9e2c-4704-8b8c-0cfc062d0acf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_8b572b80-9b26-45f4-bc62-4a78791de845" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_e7a380a9-9e2c-4704-8b8c-0cfc062d0acf" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_8b572b80-9b26-45f4-bc62-4a78791de845" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_8b572b80-9b26-45f4-bc62-4a78791de845_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_8b572b80-9b26-45f4-bc62-4a78791de845" xlink:to="loc_us-gaap_SegmentDomain_8b572b80-9b26-45f4-bc62-4a78791de845_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_40d3f1ca-0909-4c79-ad3a-3e6aabc85b0d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_8b572b80-9b26-45f4-bc62-4a78791de845" xlink:to="loc_us-gaap_SegmentDomain_40d3f1ca-0909-4c79-ad3a-3e6aabc85b0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_IndustrialMember_b7407179-1194-4834-a5f8-79975154dc9d" xlink:href="uls-20250331.xsd#uls_IndustrialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_40d3f1ca-0909-4c79-ad3a-3e6aabc85b0d" xlink:to="loc_uls_IndustrialMember_b7407179-1194-4834-a5f8-79975154dc9d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_ConsumerMember_db1ac945-2f6f-46a9-9e95-eca66577b4e2" xlink:href="uls-20250331.xsd#uls_ConsumerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_40d3f1ca-0909-4c79-ad3a-3e6aabc85b0d" xlink:to="loc_uls_ConsumerMember_db1ac945-2f6f-46a9-9e95-eca66577b4e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_SoftwareAndAdvisoryMember_8b662a4d-c94c-49a7-86d4-dfbd648f886b" xlink:href="uls-20250331.xsd#uls_SoftwareAndAdvisoryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_40d3f1ca-0909-4c79-ad3a-3e6aabc85b0d" xlink:to="loc_uls_SoftwareAndAdvisoryMember_8b662a4d-c94c-49a7-86d4-dfbd648f886b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_cd168142-be3d-4977-8512-0eabcf54d69e" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_e7a380a9-9e2c-4704-8b8c-0cfc062d0acf" xlink:to="loc_srt_ConsolidationItemsAxis_cd168142-be3d-4977-8512-0eabcf54d69e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_cd168142-be3d-4977-8512-0eabcf54d69e_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_cd168142-be3d-4977-8512-0eabcf54d69e" xlink:to="loc_srt_ConsolidationItemsDomain_cd168142-be3d-4977-8512-0eabcf54d69e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_a1172271-0bce-4a7a-b5a8-dfb0ccd6e60c" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_cd168142-be3d-4977-8512-0eabcf54d69e" xlink:to="loc_srt_ConsolidationItemsDomain_a1172271-0bce-4a7a-b5a8-dfb0ccd6e60c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_c6461bd6-8d74-4e90-a4d6-5c6d020fb25c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_a1172271-0bce-4a7a-b5a8-dfb0ccd6e60c" xlink:to="loc_us-gaap_OperatingSegmentsMember_c6461bd6-8d74-4e90-a4d6-5c6d020fb25c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_15d0bffc-43c3-4c19-9fb9-28562b84aba6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_a1172271-0bce-4a7a-b5a8-dfb0ccd6e60c" xlink:to="loc_us-gaap_CorporateNonSegmentMember_15d0bffc-43c3-4c19-9fb9-28562b84aba6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_18cc3fea-d514-40e5-92c3-449f0d71c88a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3cfd2073-1165-4018-8a98-483a7ca9f99d" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_18cc3fea-d514-40e5-92c3-449f0d71c88a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_EmployeeCompensation_c043517d-a8d9-4850-af50-469ff18c8748" xlink:href="uls-20250331.xsd#uls_EmployeeCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3cfd2073-1165-4018-8a98-483a7ca9f99d" xlink:to="loc_uls_EmployeeCompensation_c043517d-a8d9-4850-af50-469ff18c8748" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_uls_ServicesAndMaterials_ee0ecb96-71cb-4c26-b3e2-f3d85f888d67" xlink:href="uls-20250331.xsd#uls_ServicesAndMaterials"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3cfd2073-1165-4018-8a98-483a7ca9f99d" xlink:to="loc_uls_ServicesAndMaterials_ee0ecb96-71cb-4c26-b3e2-f3d85f888d67" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_60f17056-5e74-458e-89c6-be359951a438" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3cfd2073-1165-4018-8a98-483a7ca9f99d" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_60f17056-5e74-458e-89c6-be359951a438" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_900fc543-231b-465b-a69b-96d9b8fa79eb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3cfd2073-1165-4018-8a98-483a7ca9f99d" xlink:to="loc_us-gaap_OperatingIncomeLoss_900fc543-231b-465b-a69b-96d9b8fa79eb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_ba53d8ec-de22-4c99-9b0b-4691acb29ee6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3cfd2073-1165-4018-8a98-483a7ca9f99d" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_ba53d8ec-de22-4c99-9b0b-4691acb29ee6" xlink:type="arc" order="5"/>
  </link:definitionLink>
</link:linkbase>
