# Definition:Domain (Set Theory)/Binary Operation

Let $\circ: S \times S \to T$ be a binary operation.
The domain of $\circ$ is the set $S$ and can be denoted $\operatorname{Dom} \left({\circ}\right)$.
This definition can be considered as the same as that for the domain of a mapping, where the domain would be defined as $S \times S$.