A

total function for which there is an

effective method of computing its output, for every input.

A computable function can also be defined as one that can be computed by an algorithm, or (equivalently), by a Turing Machine.
For example:

**f(n) = n + 1 ** is a computable function. The algorithm that solves it takes the input and adds one. (How simple is that?)

**Turing's Halting Problem** is an incomputable function.