Divisibility is a mathematical concept that refers to the ability of one integer to be divided by another without leaving a remainder. For example, if an integer ( a ) can be expressed as ( a = b \times k ) for some integer ( k ), then ( a ) is said to be divisible by ( b ). Common tests for divisibility include rules for small numbers like 2, 3, 5, and 10, which help quickly determine if one number can be divided by another.