[Vince]

This is the modulus and calculates the remainder of a division. It is frequently used to check if a number is odd or even.

6 / 2 returns a whole number (3), and thus the remainder is 0. (3 * 2 = 6).
6 / 4 returns 1 and the remainder is 2. (1 * 4 + 2 = 6).