An arithmetic sequence is a list of numbers in which each term after the first is found by adding a constant value, known as the common difference, to the previous term. For example, in the sequence 2, 5, 8, 11, the common difference is 3. This pattern continues indefinitely, allowing for easy prediction of future terms. The formula for the nth term of an arithmetic sequence is given by a_n = a_1 + (n - 1)d, where a_n is the nth term, a_1 is the first term, n is the term number, and d is the common difference. This formula helps in calculating any term in the sequence without listing all previous terms.