A semigroup is a set {displaystyle S} S together with a binary operation " {displaystyle cdot } cdot " (that is, a function {displaystyle cdot :S imes S
ightarrow S} cdot:S imes S
ightarrow S) that satisfies the associative property:
For all {displaystyle a,b,cin S} a,b,cin S, the equation {displaystyle (acdot b)cdot c=acdot (bcdot c)} (acdot b)cdot c = acdot(bcdot c) holds.
More succinctly, a semigroup is an associative magma.