A set of one or more axioms that partially or sufficiently specify the meaning of a SNOMED CT concept.

Concept definitions are represented in two ways in SNOMED CT release files:
- As a stated view represented by axioms that conform to the OWL Functional Syntax distributed in the OWL Expression Reference Set file.
- As an inferred view represented by defining relationships that are distributed in the relationship file. The inferred view is generated by applying description logic classification to the stated view.
Concept definitions include two distinct elements
- Axioms that assert that a concept is a subtype of one or more other concepts. In the inferred view these are represented as subtype relationships.
- Axioms that assert characteristics of a concept that distinguish it from its supertypes. In the inferred view these are represented as attribute relationships.

Prior to July 2018 the stated view of concept definitions were represented by relationships in the Stated Relationships file. During a transitional period between July 2018 and July 2019 the OWL reference sets were introduced. Since the end of that transitional period in July 2019, the stated relationship file is no longer maintained or distributed. More information on the earlier representation of the stated view is provided in a historical note on Representation of the Logical Model - Before July 2018.

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