An abstraction; a general idea inferred or derived from specific instances. (Oxford Dictionaries Online 2012)
Oxford Dictionaries Online S.v. "Concept" Accessed February 20, 2012. http://oxforddictionaries.com/definition/concept.
A concept is an abstraction; a general idea inferred or derived from specific instances. For example, by viewing a pet dog, one can infer that there are other dogs of that “type.” Hence, from this observation (or perhaps a set of observations) the concept of a dog is developed in one's mind. Concepts are bearers of meaning, as opposed to agents of meaning and can only be thought about, or designated, by means of a name.
Lawson, H., and J.N. Martin. 2008. "On the Use of Concepts and Principles for Improving Systems Engineering Practice". Proceedings of the 18th Annual International Council on Systems Engineering (INCOSE) International Symposium, 5-19 June 2008, Utrecht, The Netherlands.