Elements
I quite like this:
One of the important perceptions of category theory is that an arrow x : T → A in a category can be regarded as an element of A defined over T. The idea is that x is a variable element of A, meaning about the same thing as the word “quantity†in such sentences as, “The quantity x2 is nonnegativeâ€, found in older calculus books.
—Toposes, Triples and Theories, Michael Barr and Charles Wells, Version 1.1, 2002