What is the definition of a function?

A function in algebra is such a relationship, in which every input has a single output. It is usually written down as f(x), where x is the input. For example, if f(x) = x+1. In this case, if x (the input) equals 10, the output will be 11, and so on. f(10) = 11; f(15) = 16; f(24)=25, etc.