\begin{definition}[Definition:Function]
The process which is symbolised by an operation is called a '''function'''.
The operand(s) of the operation can be considered to be the input(s).
The output of the '''function''' is whatever the operation is defined as doing with the operand(s).
A '''function''' is in fact another name for a mapping, but while the latter term is used in the general context of set theory and abstract algebra, the term '''function''' is generally reserved for mappings between sets of numbers.
\end{definition}