What is FizzBuzz?

FizzBuzz is a simple coding challenge, often described as a code kata. The objective of FizzBuzz is to create a program with the following specification:

The program can be passed a number.
When passed a number that is a multiple of 3, the program returns the message 'Fizz'.
When passed a number that is a multiple of 5, the program returns the message 'Buzz'.
When passed a number that is a multiple of both 3 and 5, the program ignores the previous 2 rules and returns the message 'FizzBuzz'.
In all other cases, the program simply returns the given number.