It's a simple coding test that asks you to write s program that prints Fizz, Buzz or FizzBuzz, usually depending on the multiple of some number. I.e. multiple of 3 print fizz, multiple of 5 print buzz, multiples of both 5 and 3 print fizzbuzz. Usually it will ask you to do this for numbers from 1 to 100, or something like that.

It's basically a way to weed out people who don't know how to write any code.