What are multiples and diVisors: https://youtu.be/ij5_vWBxZoU
A multiple of a given integer is the product of that integer with some other integer. Thus is a multiple of only if can be written in the form , where and are integers. (In this case, is a multiple of , as well).
Every nonzero integer has an infinite number of multiples. As an example, some of the multiples of 15 are 15, 30, 45, 60, and 75.
An equivalent phrasing is that is a multiple of exactly when is divisble by .
In Modular Arithmetic, multiples of the modulus, are congruent to 0