1. The action of functioning or the fact of being active or in effect.
2. An active process; a discharge of a function.
3. An act of surgery performed on a patient.
4. An organized activity involving a number of people.
5. A business organization; a company.
6. A process in which a number, quantity, expression, etc., is altered or manipulated according to set formal rules, such as those of addition, multiplication, and differentiation.
Plural Noun: Operations
The doctor did the operation well.