1) A defined action; namely, the act of obtaining a result from one or more operands in accordance with a rule that completely specifies the result of any permitted combination of operands. 2) The set of such acts specified by a rule, or the rule itself. 3) The act specified by a single computer instruction. 4) A programme step undertaken or executed by a computer, e.g., addition, multiplication, extraction, comparison, shift, transfer, etc. 5) The specific action performed by a logic element.