The usage and significance of MOD are: a≡b(mod c) means that a and b have the same remainder after being divided by c, which means that a and b are congruent, and mod is c, for example, a mod b=c means that a is divided by b and the remainder is c, for example, what is the unit of100th power of 2? It can be written as 2 100 ≡ 6. (mod 10) Especially in the decimal system, the decimal system is represented by "mod". Mod n is pronounced "modulo n"