For any integers a and b, a is a mulitple of b if a third integer exists such that a = b x c.

Example: 14 = 7 x 2, 49 = 7 x 7 and 70 = 7 x 10. So 14, 49 and 70 are all multiples of 7.

-21 is also a multiple of 7 since -21 = 7(-3).