1 A function from Sm (see Cartesian product) into S itself, where S is some set specific to the function. Such a function is usually referred to as an m-ary or m-adic operation over S, m being some natural number, sometimes referred to as the arity of the operation. The most common operations are the dyadic (or binary) operations that map S × S into S and the monadic (or unary) operations that map S into S. The case where the arity is zero gives the so-called nullary operations, which correspond simply to elements of S. There is also a more general kind of operation that involves more than one set. For example, in a finite-state automaton the next state depends on the current input symbol and the current state, and is thus given by a dyadic operation from I × Q into Q, where I is the set of input symbols and Q the set of states. See also logic operation, arithmetic operation, operations on sets.
2Another name for instruction (in a computer), as designated by an operation code.
3 in a programming language. Whatever is carried out by an operator (def. 2), or, more generally, anything that can take place within a program: a declaration, an assignment statement, a selection, a loop, the call of a function, and so on.