\begin{definition}[Definition:Series/Tail]
Let $\struct {S, \circ}$ be a semigroup.
Let $\sequence {a_n}$ be a sequence in $S$.
Let $N \in \N$.
The expression $\ds \sum_{n \mathop = N}^\infty a_n$ is known as a '''tail''' of the '''series''' $\ds \sum_{n \mathop = 1}^\infty a_n$.
Category:Definitions/Series
\end{definition}