operation

An operation is a function which maps zero or more inputs (operands) to a well-defined output value. The number of operands is the arity of the operation.

Formally,
an $n$-ary operation $\omega$ on a set $X$ is a function $\omega :X^n\to X$:

where the fixed non-negative integer $n$ (the number of operands) is the arity of the operation,
and $\times$ is the Cartesian product.

Nullary operations (of arity 0) are constant.

Unary operations (of arity 1) involve only one value. Examples include: negation (inverse element), trigonometric functions

Binary operations (of arity 2) involve turning two values into one value. Examples include: addition, subtraction, multiplication, division, exponentiation, logic operations, composition, convolution, set operations

Ternary operations (of arity 3) map a set of three values into one value. Examples include: scalar triple product