Center

The center of a group $G$ is a subgroup defined by

$$Z(G)=\{A\in G|AB=BA\forall B\in G\}$$

($Z$ ist aus Deutsch “Zentrum”)

Example

An element $A\in Z(SO(3))$ commutes with all elements of $SO(3)$, and in particular with all elements of the maximal torus ${\mathbb{T}}^1$