An arithmetic series is the sum of the terms in an arithmetic sequence, where each term increases or decreases by a constant value called the common difference. For example, in the sequence 2, 4, 6, 8, the common difference is 2. The series can be expressed as the sum of these terms, such as 2 + 4 + 6 + 8. To find the sum of an arithmetic series, you can use the formula S_n = \fracn2 (a + l) , where S_n is the sum, n is the number of terms, a is the first term, and l is the last term. This formula simplifies the process of calculating the total of the series.