In the original, "abstract" is redundant, "thing or things" is not defensible, and "basic unit" asserts clarity it does not provide.
An idea. In information modelling, a concept is represented as a word or phrase in order to support human understanding, but may also be represented with a concept identifier in order to bind it to a controlled terminology or ontology.
See also: binding --Jay Lyle 08:00 14 February 2012 (EST)
Previously: A Concept is an abstract thought about a thing, or things, in the world. It the basic unit of communication and each concept represents an atomic unit of thought that references a concrete or abstract thing. A single concept may be represented using either a single code, a defining expression or a structure of other concepts from which this concept is defined.
In SNOMED CT, each concept is uniquely identified by a concept ID, and a Fully Specified Name (FSN). SNOMED CT concepts may be formally defined in terms of their relationships with other concepts.
--Jay Lyle 17:35, 23 February 2012 (EST)