A function often referred to as the modulus function in computer science, also known to many as the % operator. It basically returns the remainder of a number when divided by it's modulus, like 6 mod 5 is 1. The range of the function is from 0 to n-1. The domain is unlimited, as long as the set is the set of all positive integers including 0. The mod-n function is useful for computer science applications such as hashing and finding the remainder.