A permutation, often referred to as a perm, is an arrangement of items in a specific order. For example, if you have three letters, A, B, and C, the different ways to arrange these letters are ABC, ACB, BAC, BCA, CAB, and CBA. The total number of permutations depends on the number of items being arranged. Permutations are commonly used in mathematics and computer science to solve problems involving arrangements and combinations. The formula for calculating the number of permutations of n distinct objects is n!, which means n factorial. For instance, 3! equals 6, representing the six arrangements of three items.