Divisibility rules are simple guidelines that help determine whether one number can be divided by another without leaving a remainder. For example, a number is divisible by 2 if its last digit is even (0, 2, 4, 6, or 8). Similarly, a number is divisible by 5 if its last digit is either 0 or 5. These rules can make calculations easier, especially with larger numbers. For instance, a number is divisible by 3 if the sum of its digits is divisible by 3. Understanding these rules can help in solving problems in math and arithmetic more efficiently.