Commutative operation

Let $A$ and $B$ be two sets and $*\colon A\times A\longrightarrow B$ be an operation.

Then $*$ is said to be commutative if, for all $x,y\in A$, the identity $x*y=y*x$ holds.

Examples:
$\bullet$ The addition (so $*=+$) defined on the sets of integers (so $A=B=\Z$) is commutative. Thus, for instance, we have $2+5=7=5+2$. As well as any addition defined on a ring.
$\bullet$ The product of two squared matrices is not commutative.