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A set of textual descriptions are assigned to every concept. These provide the human readable form of a concept. Two types of description are used to represent every concept - Fully Specified Name (FSN) and Synonym.
The FSN represents a unique, unambiguous description of a concept's meaning. The FSN is not intended to be displayed in clinical records, but is instead used to disambiguate the distinct meaning of each different concept. This is particularly useful when different concepts are referred to by the same commonly used word or phrase. Each concept can have only one FSN in each language or dialect.
A synonym represents a term that can be used to display or select a concept . A concept may have several synonyms. This allows users of SNOMED CT to use the terms they prefer to refer to a specific clinical meaning. Concepts can have multiple synonyms, and the associated terms are not necessarily unique – thus two concepts can have the same synonym term. Interpretation of a synonymous term therefore depends on the concept identifier.
Each concept has one synonym which is marked as |preferred | in a given language, dialect, or context of use. This is known as the "preferred term" and is a word or phrase commonly used by clinicians to name that concept. In each language, dialect or context of use, one and only one synonym can be marked as | preferred |. Any number of other synonyms that are valid in a language, dialect or context of use can be marked as | acceptable |.

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In SNOMED CT every concept is specified as either fully defined or primitive.
A concept is fully-defined if its defining characteristics are sufficient to distinguish its meaning from other similar concepts. One example is that the concept |acute disease| is fully-defined by its two defining relationships . The first  relationship is |is a||disease| and the second relationship is |clinical course||sudden onset AND/OR short duration|. Stating that this concept is fully-defined means that any concept that |is a||disease| and has a |clinical course| of |sudden onset AND/OR short duration| is a subtype of this concept (or the concept itself).
A concept is primitive (not fully-defined) if its defining characteristics are not sufficient to uniquely distinguish its meaning from other similar concepts. One example is that the primitive concepts |disease| and |drug action| share the same defining characteristics : namely a relationship of type |is a| to the concept |clinical finding|. This is despite the fact that the concepts |disease| and |drug action| represent different clinical ideas.

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