A functor is a certain kind of function (Theres a pedantic point to be made but it's mostly irrelevant). However, most functions are not functors. To give a si

A functor is a certain kind of function (Theres a pedantic point to be made but it's mostly irrelevant). However, most functions are not functors. To give a simpler example, we say a function, f, is monotone when for x<y, f(x)<f(y); that is, it preserves order. Every monotone function is obviously a function, but functions like x^2 are not monotone. Basically a functor is a function which preserves some other properties. I wont go into detail as many have before me, but thats the gist.