Definition:Operation/Binary Operation/Infix Notation

Notation
Let $S, T, U$ be sets. Let $\circ: S \times T \to U$ be a binary operation.

When $\circ \left ({x, y}\right) = z$, it is common to put the symbol for the operation between the two operands:
 * $z = x \circ y$

This convention is called infix notation.