模除是一种不具交换性的二元运算。

当，q是整数，并使其达到最大，此时我们说a模除b等于r。(r为非负数)

以数学式子表示：a模除b。

例如要计算100模除16，由于100/16是一个大于6且不大于7的数，取q=6。100-16*6=4，而4就是答案。

In computing, the modulo operation finds the remainder after division of one number by another (sometimes called modulus).

Given two positive numbers, a (the dividend) and n (the divisor), a modulo n (abbreviated as a mod n) is the remainder of the Euclidean division of a by n. For instance, the expression "5 mod 2" would evaluate to 1 because 5 divided by 2 leaves a quotient of 2 and a remainder of 1, while "9 mod 3" would evaluate to 0 because the division of 9 by 3 has a quotient of 3 and leaves a remainder of 0; there is nothing to subtract from 9 after multiplying 3 times 3. (Note that doing the division with a calculator will not show the result referred to here by this operation; the quotient will be expressed as a decimal fraction.)