\begin{definition}[Definition:Center (Abstract Algebra)/Semigroup]
The '''center of a semigroup''' $\struct {S, \circ}$, denoted $\map Z S$, is the subset of elements in $S$ that commute with every element in $G$.
Symbolically:
:$\map Z S = \set {s \in S: \forall x \in S: s \circ x = x \circ s}$
\end{definition}