The remainder of the quotient of two numbers (usually integers).
Primes or prime numbers are integers greater than 1 which are divisible only by themselves and 1, i.e.: 2, 3, 5, 7, 11, ..
"It is perfectly possible to use rsa with a modulus n that is composed of more than two primes factors p and q but two things have to be noted"
from question "Integer factorization and cryptography"