Definition of "concept"

The words conception, concept, notion, should be limited to the thought of what can not be represented in the imagination; as, the thought suggested by a general term.

1855, Thomas Reid, Sir W. Hamilton, James Walker, “Essay IV. Of Conception”, in Essays on the Intellectual Powers of Man‎

Frege's concepts are very nearly propositional functions in the modern sense. Frege explicitly recognizes them as functions. Like Peirce's rhema, a concept is unsaturated. They are in some sense incomplete. Although Frege never gets beyond the metaphorical in his description of the incompleteness of concepts and other functions, one thing is clear: the distinction between objects and functions is the main division in his metaphysics. There is something special about functions that makes them very different from objects.

2011 July 20, Edwin Mares, “Propositional Functions”, in The Stanford Encyclopedia of Philosophy‎, retrieved 2012-07-15

Few concepts are as emotionally charged as that of race. The word conjures up a mixture of associations—culture, ethnicity, genetics, subjugation, exclusion and persecution. But is the tragic history of efforts to define groups of people by race really a matter of the misuse of science, the abuse of a valid biological concept?

2012 March-April, Jan Sapp, “Race Finished”, in American Scientist‎, volume 100, number 2, page 164