Question

Whats a function?

Answer 1

A function is a relation between inputs and outputs, where each input is related to one single output.

Answer 2

Historically , the term "function" was first used by Leibniz in 1673 to denote the dependence of one quantity on another, for example:
the area of a circle depends on its radius by the equation A=pie r^2, so we say that "A is a function of r. in general , if a quantity y depends on a quantity x in such a way that each value of x determines exactly one value of y. e.g.= (y=4x+1). (copied out of a calculus book for your own personal learning.