Commutative

Two elements $x$ and $y$ of a set $S$ are said to be commutative under a binary operation $*$ if they satisfy

$$x*y = y*x.$$

Real numbers are commutative under addition

$$x+y = y+x$$

and multiplication

$$x\cdot y = y\cdot x.$$

See also Associative, Distributive, Transitive