Ecco che cosa si trova in* WikiPedia *(versione inglese) sul concetto di operazione.
Vengono considerate "operazioni" particolari "funzioni", ma, come si vede leggendo il testo,
la definzione di operazione non è affatto standardizzata.

An** operation **ω is a* function *of the form ω: V→Y,
where V ⊂ X1×…×Xk.

The sets Xk are called the* domains *of the operation,
the set Y is called the* codomain *of the operation, and the fixed non-negative integer k (the number of arguments) is called the type or* arity *of the operation.
Thus a* unary operation *has arity one, and a* binary operation *has arity two. An operation of arity zero, called a* nullary *operation,
is simply an element of the codomain Y. An operation of arity* k *is called a k-ary operation.
Thus a k-ary operation is a (k+1)-ary* relation *that is functional on its first k domains.

The above describes what is usually called a* finitary *operation, referring to the finite number of arguments (the value k).
There are obvious extensions where the arity is taken to be an infinite* ordinal *or *cardinal*, or even an arbitrary set indexing the arguments.

Often, use of the term operation implies that the domain of the function is a power of the codomain
(i.e. the *Cartesian product* of one or more copies of the codomain), although this is by no means universal,
as in the example of multiplying a vector by a scalar.

In *WolframAlpha* viene considerato un concetto più restrittivo:

Let A be a set. An operation on A is a* function *from a power of A into A.
More precisely, given an ordinal number α, a function F from A^{α} into A is an α-ary operation on A. If α = n is a finite ordinal,
then the n-ary operation F is a finitary operation on A.