A ring of integers derived from the set of all integers according to the following rule: Let N be an integer greater than 1, and A and B be two other integers; if N is a factor of A·B, then A is said to be congruent to a B modulo-N.

• 由全体整数的集合按下列规则产生的整数环:设N为大于1的整数,a和B是两个其它整数,若N是a·B的因子,则称a与B是模N的同余式。