The modulo operation is used to find the remainder (or leftover) after a division operation. It is commonly used in programming, denoted by the % symbol. Mathematically, it is denoted by \"a mod n\", where a is the dividend (the number to be divided into), n is the divisor (the number to divide into the dividend), and the mod being the leftover after the operation. Modulo actually represents the equation M = a * n + r, so keep that in mind when find the mod of negative numbers!