This code system http://hl7.org/fhir/concept-map-relationship defines the following codes:

LvlCodeDisplayDefinition
1related-to Related ToThe concepts are related to each other, but the exact relationship is not known.
2  equivalent EquivalentThe definitions of the concepts mean the same thing.
2  source-is-narrower-than-target Source Is Narrower Than TargetThe source concept is narrower in meaning than the target concept.
2  source-is-broader-than-target Source Is Broader Than TargetThe source concept is broader in meaning than the target concept.
1not-related-to Not Related ToThis is an explicit assertion that the target concept is not related to the source concept.
<status value="draft"/><experimental value="false"/><date value="2023-03-26T15:21:02+11:00"/><description value="The relationship between concepts."/><jurisdiction><coding><system value="http://unstats.un.org/unsd/methods/m49/m49.htm"/><code value="001"/><display value="World"/></coding></jurisdiction><caseSensitive value="true"/><valueSet value="http://hl7.org/fhir/ValueSet/concept-map-relationship"/><content value="complete"/><concept><code value="related-to"/><display value="Related To"/><definition value="The concepts are related to each other, but the exact relationship is not known."/><concept><code value="equivalent"/><display value="Equivalent"/><definition value="The definitions of the concepts mean the same thing."/></concept><concept><code value="source-is-narrower-than-target"/><display value="Source Is Narrower Than Target"/><definition value="The source concept is narrower in meaning than the target concept."/></concept><concept><code value="source-is-broader-than-target"/><display value="Source Is Broader Than Target"/><definition value="The source concept is broader in meaning than the target concept."/></concept></concept><concept><code value="not-related-to"/><display value="Not Related To"/><definition value="This is an explicit assertion that the target concept is not related to the source concept."/></concept></CodeSystem>