What does "operation" mean?

Additional senses

1. 2.That which is operated or accomplished; an effect brought about in accordance with a definite plan; as, military or naval operations.
2. 3.Effect produced; influence. [Obs.] The bards . . . had great operation on the vulgar. Fuller.
3. 4.(Math.) Something to be done; some transformation to be made upon quantities, the transformation being indicated either by rules or symbols.
4. 5.(Surg.) Any methodical action of the hand, or of the hand with instruments, on the human body, to produce a curative or remedial effect, as in amputation, etc. Calculus of operations. See under Calculus.