A series is a group of similar things that are all related to the same topic.

In mathematics, a series is the adding of a sequence, a list of (usually never-ending) mathematical objects (such as numbers). It is sometimes written as \displaystyle{ \textstyle \sum_{n=i}^k a_n }, which is another way of writing \displaystyle{ a_i + \cdots + a_k }.

For example, the series \displaystyle{ \textstyle \sum_{n=0}^{\infty} \frac{1}{2^n} } corresponds to the following sum:

\displaystyle{ 1 + \frac12 + \frac14 + \frac18 + \frac1{16} + \frac1{32} + \frac1{64} + \frac1{128} + \ldots }