When one number can be divided by another and the result is an exact whole number.

Example: 15 is divisible by 3, because 15 ÷ 3 = 5 exactly

But 9 is not divisible by 2 because 9 ÷ 2 is 4 with 1 left over.

Example: 15 is divisible by 3, because 15 ÷ 3 = 5 exactly

But 9 is not divisible by 2 because 9 ÷ 2 is 4 with 1 left over.