What is a callback function?

Question

What is a callback function?

Answer 1

This makes callbacks sound like return statements at the end of methods.

I'm not sure that's what they are.

I think Callbacks are actually a call to a function, as a consequence of another function being invoked and completing.

I also think Callbacks are meant to address the originating invocation, in a kind of "hey! that thing you asked for? I've done it - just thought I would let you know - back over to you".