an act or instance, process, or manner of functioning or operating.

the state of being operative (usually prec. by in or into )

a rule no longer in operation.

the power to act; efficacy, influence, or force.

the exertion of force, power, or influence; agency

the operation of alcohol on the mind.

a process of a practical or mechanical nature in some form of work or production

a delicate operation in watchmaking.

a course or procedure of productive or industrial activity

building operations.

a particular process or course

mental operations.

a business transaction, esp. one of a speculative nature; deal

a shady operation.

a business, esp. one run on a large scale

a multinational operation.

Surgery . a procedure aimed at restoring or improving the health of a patient, as by correcting a malformation, removing diseased parts, implanting new parts, etc.

Mathematics .

a mathematical process, as addition, multiplication, or differentiation.

the action of applying a mathematical process to a quantity or quantities.

Military .

a campaign, mission, maneuver, or action.

Usually, operations. the conduct of a campaign, mission, etc.

operations, a headquarters, office, or place from which a military campaign, air traffic to and from an airfield, or any of various other activities, is planned, conducted, and controlled.

operations, the people who work at such a headquarters.