noun: (object-oriented programming) A function object.
noun: (category theory) A category homomorphism; a morphism from a source category to a target category which maps objects to objects and arrows to arrows, in such a way as to preserve domains and codomains (of the arrows) as well as composition and identities.
noun: (functional programming) A structure allowing a function to apply within a generic type, in a way that is conceptually similar to a functor in category theory.
