An arithmetic progression (AP) is a sequence of numbers in which the difference between consecutive terms is constant. This difference is called the "common difference." For example, in the sequence 2, 5, 8, 11, the common difference is 3, as each term increases by 3 from the previous one. Arithmetic progressions can be represented by the formula a_n = a_1 + (n-1)d , where a_n is the nth term, a_1 is the first term, d is the common difference, and n is the term number. APs are widely used in various fields, including mathematics, finance, and computer science.