1. The act of making something carry out its function, or controlling or managing the way it works.
2. The state of functioning or of being in effect. The ban on playing loud music will bput into operation starting next week.
3. Something that is carried out; especially, something difficult or complex.
4. Any surgical procedure; that is, one carried out to repair damage to a body part.
5. An organized campaign, maneuver, or other form of action, especially one carried out by rescue personnel, the police, or diplomatic personnel.
6. An action conducted by military forces that can range in scope from a reconnaissance mission to an entire campaign: "Operation Desert Storm".
7. A mathematical process in which entities are derived from others through the application of rules; for example, subtraction, multiplication, or differentiation.
8. A series of actions performed by a computer, defined by an instruction and forming part of a computer program.
9. A business deal or financial transaction.
10. An illegal, dishonest, or underhanded business; for example, he got involved in a shady gambling operation.

A government, or military, intelligence operation so planned and executed so as to insure concealment.