<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<link:linkbase xmlns:ns6="http://www.sec.gov/edgar/common" xmlns:ns5="http://www.sec.gov/edgar/singlefilersc" xmlns:ns8="http://www.sec.gov/edgar/coregsc" xmlns:ns7="http://www.sec.gov/edgar/sccommon" xmlns:ns9="http://www.sec.gov/edgar/bulkfiling" xmlns:ns11="http://xbrl.org/2006/xbrldi" xmlns:ns10="http://www.sec.gov/edgar/feecommon" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:ns4="http://www.xbrl.org/2003/instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ns3="http://www.xbrl.org/2003/XLink">
    <link:roleRef roleURI="http://xbrl.sec.gov/oef/role/SeriesOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#SeriesOnly"/>
    <link:roleRef roleURI="http://xbrl.sec.gov/oef/role/ClassOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#ClassOnly"/>
    <link:roleRef roleURI="http://xbrl.sec.gov/rr/role/RiskOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#RiskOnly"/>
    <link:roleRef roleURI="http://xbrl.sec.gov/rr/role/PerformanceMeasureOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#PerformanceMeasureOnly"/>
    <link:roleRef roleURI="http://www.fidelity.com/role/DocumentInformation" xlink:type="simple" xlink:href="fmr-20261030.xsd#role_DocumentInformation"/>
    <link:roleRef roleURI="http://www.fidelity.com/role/RiskSummaryS000005131_FidelityAdvisorLimitedTermBondFund-AMCIZPRO" xlink:type="simple" xlink:href="fmr-20261030.xsd#role_RiskSummaryS000005131_FidelityAdvisorLimitedTermBondFund-AMCIZPRO"/>
    <link:roleRef roleURI="http://www.fidelity.com/role/DisclosureDetailS000005131_FidelityAdvisorLimitedTermBondFund-AMCIZPRO" xlink:type="simple" xlink:href="fmr-20261030.xsd#role_DisclosureDetailS000005131_FidelityAdvisorLimitedTermBondFund-AMCIZPRO"/>
    <link:roleRef roleURI="http://www.fidelity.com/role/RiskSummaryS000005131_FidelityAdvisorLimitedTermBondFund-RetailPRO" xlink:type="simple" xlink:href="fmr-20261030.xsd#role_RiskSummaryS000005131_FidelityAdvisorLimitedTermBondFund-RetailPRO"/>
    <link:roleRef roleURI="http://www.fidelity.com/role/DisclosureDetailS000005131_FidelityAdvisorLimitedTermBondFund-RetailPRO" xlink:type="simple" xlink:href="fmr-20261030.xsd#role_DisclosureDetailS000005131_FidelityAdvisorLimitedTermBondFund-RetailPRO"/>
    <link:roleRef roleURI="http://www.fidelity.com/role/RiskSummaryS000005133_FidelityAdvisorMortgageSecuritiesFund-AMCIZPRO" xlink:type="simple" xlink:href="fmr-20261030.xsd#role_RiskSummaryS000005133_FidelityAdvisorMortgageSecuritiesFund-AMCIZPRO"/>
    <link:roleRef roleURI="http://www.fidelity.com/role/DisclosureDetailS000005133_FidelityAdvisorMortgageSecuritiesFund-AMCIZPRO" xlink:type="simple" xlink:href="fmr-20261030.xsd#role_DisclosureDetailS000005133_FidelityAdvisorMortgageSecuritiesFund-AMCIZPRO"/>
    <link:roleRef roleURI="http://www.fidelity.com/role/RiskSummaryS000005133_FidelityAdvisorMortgageSecuritiesFund-RetailPRO" xlink:type="simple" xlink:href="fmr-20261030.xsd#role_RiskSummaryS000005133_FidelityAdvisorMortgageSecuritiesFund-RetailPRO"/>
    <link:roleRef roleURI="http://www.fidelity.com/role/DisclosureDetailS000005133_FidelityAdvisorMortgageSecuritiesFund-RetailPRO" xlink:type="simple" xlink:href="fmr-20261030.xsd#role_DisclosureDetailS000005133_FidelityAdvisorMortgageSecuritiesFund-RetailPRO"/>
    <link:roleRef roleURI="http://www.fidelity.com/role/RiskSummaryS000085243_FidelityLimitedTermSecuritizedCompletionFund-PRO" xlink:type="simple" xlink:href="fmr-20261030.xsd#role_RiskSummaryS000085243_FidelityLimitedTermSecuritizedCompletionFund-PRO"/>
    <link:roleRef roleURI="http://www.fidelity.com/role/DisclosureDetailS000085243_FidelityLimitedTermSecuritizedCompletionFund-PRO" xlink:type="simple" xlink:href="fmr-20261030.xsd#role_DisclosureDetailS000085243_FidelityLimitedTermSecuritizedCompletionFund-PRO"/>
    <link:roleRef roleURI="http://www.fidelity.com/role/RiskSummaryS000062808_FidelitySeriesInvestmentGradeSecuritizedFund-PRO" xlink:type="simple" xlink:href="fmr-20261030.xsd#role_RiskSummaryS000062808_FidelitySeriesInvestmentGradeSecuritizedFund-PRO"/>
    <link:roleRef roleURI="http://www.fidelity.com/role/DisclosureDetailS000062808_FidelitySeriesInvestmentGradeSecuritizedFund-PRO" xlink:type="simple" xlink:href="fmr-20261030.xsd#role_DisclosureDetailS000062808_FidelitySeriesInvestmentGradeSecuritizedFund-PRO"/>
    <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-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/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/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
    <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:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/oef/role/SeriesOnly" xlink:title="050020 - Document - Series">
        <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis" xlink:label="LegalEntityAxis"/>
        <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain" xlink:label="EntityDomain"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_S000062808Member" xlink:label="fmr_S000062808Member"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EntityDomain" xlink:to="fmr_S000062808Member" order="10.1"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_S000005133Member" xlink:label="fmr_S000005133Member"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EntityDomain" xlink:to="fmr_S000005133Member" order="10.2"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_S000005131Member" xlink:label="fmr_S000005131Member"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EntityDomain" xlink:to="fmr_S000005131Member" order="10.3"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_S000085243Member" xlink:label="fmr_S000085243Member"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EntityDomain" xlink:to="fmr_S000085243Member" order="10.4"/>
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/oef/role/ClassOnly" xlink:title="050030 - Document - Class">
        <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_ShareClassDomain" xlink:label="ShareClassDomain"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000203455Member" xlink:label="fmr_C000203455Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000014129Member" xlink:label="fmr_C000014129Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000014042Member" xlink:label="fmr_C000014042Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000014045Member" xlink:label="fmr_C000014045Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000014044Member" xlink:label="fmr_C000014044Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000014046Member" xlink:label="fmr_C000014046Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000204997Member" xlink:label="fmr_C000204997Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000132104Member" xlink:label="fmr_C000132104Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000014032Member" xlink:label="fmr_C000014032Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000014035Member" xlink:label="fmr_C000014035Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000014034Member" xlink:label="fmr_C000014034Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000014036Member" xlink:label="fmr_C000014036Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000204996Member" xlink:label="fmr_C000204996Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_C000250211Member" xlink:label="fmr_C000250211Member"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000203455Member" order="2"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000014129Member" order="3"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000014042Member" order="4"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000014045Member" order="5"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000014044Member" order="6"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000014046Member" order="7"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000204997Member" order="8"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000132104Member" order="9"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000014032Member" order="10"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000014035Member" order="11"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000014034Member" order="12"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000014036Member" order="13"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000204996Member" order="14"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="fmr_C000250211Member" order="15"/>
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/rr/role/RiskOnly" xlink:title="050010 - Document - Risk">
        <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_AllRisksMember" xlink:label="AllRisksMember"/>
        <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_RiskAxis" xlink:label="RiskAxis"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_InterestRateChangesMember" xlink:label="InterestRateChangesMember"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="InterestRateChangesMember" order="500"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_SecuritizedDebtSecuritiesExposureMember" xlink:label="SecuritizedDebtSecuritiesExposureMember"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="SecuritizedDebtSecuritiesExposureMember" order="500.1"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_LeverageRiskMember" xlink:label="LeverageRiskMember"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="LeverageRiskMember" order="500.2"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_HighPortfolioTurnoverMember" xlink:label="HighPortfolioTurnoverMember"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="HighPortfolioTurnoverMember" order="500.3"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_ForeignExposureMember" xlink:label="ForeignExposureMember"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="ForeignExposureMember" order="500.4"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_IssuerSpecificChangesMember" xlink:label="IssuerSpecificChangesMember"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="IssuerSpecificChangesMember" order="500.5"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_PrepaymentMember" xlink:label="PrepaymentMember"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="PrepaymentMember" order="500.6"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_USGovernmentObligationsRiskMember" xlink:label="USGovernmentObligationsRiskMember"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="USGovernmentObligationsRiskMember" order="500.7"/>
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/rr/role/PerformanceMeasureOnly" xlink:title="050040 - Document - Performance Measure">
        <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_PerformanceMeasureDomain" xlink:label="PerformanceMeasureDomain"/>
        <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_AfterTaxesOnDistributionsMember" xlink:label="AfterTaxesOnDistributionsMember"/>
        <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_AfterTaxesOnDistributionsAndSalesMember" xlink:label="AfterTaxesOnDistributionsAndSalesMember"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_IndexLB371Member" xlink:label="fmr_IndexLB371Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_IndexLB001Member" xlink:label="fmr_IndexLB001Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_IndexLB006Member" xlink:label="fmr_IndexLB006Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_IndexF1871Member" xlink:label="fmr_IndexF1871Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_IndexLB087Member" xlink:label="fmr_IndexLB087Member"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_IndexIXTGBMember" xlink:label="fmr_IndexIXTGBMember"/>
        <link:loc xlink:type="locator" xlink:href="fmr-20261030.xsd#fmr_IndexLB074Member" xlink:label="fmr_IndexLB074Member"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PerformanceMeasureDomain" xlink:to="fmr_IndexLB371Member" order="5"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PerformanceMeasureDomain" xlink:to="fmr_IndexLB001Member" order="6"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PerformanceMeasureDomain" xlink:to="fmr_IndexLB006Member" order="7"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PerformanceMeasureDomain" xlink:to="fmr_IndexF1871Member" order="8"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PerformanceMeasureDomain" xlink:to="fmr_IndexLB087Member" order="9"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PerformanceMeasureDomain" xlink:to="fmr_IndexIXTGBMember" order="10"/>
        <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PerformanceMeasureDomain" xlink:to="fmr_IndexLB074Member" order="11"/>
    </link:definitionLink>
</link:linkbase>
