Meaning of “operation” - Learner’s Dictionary

operation

noun [ C ] us uk /ˌɒpərˈeɪʃən/
Happily, the operation was a complete success.She only had the operation last month but she's made a good recovery.The operation is done under anaesthetic.She's already had to endure three painful operations on her leg.Surgeons performed the operation in less than two hours.
MEDICAL TREATMENT

B1 If you have an operation, a doctor cuts your body to remove or repair part of it:

a heart/lung operation
a major/minor operation
My son's got to have an operation.
ORGANIZATION

an organization or business:

a large commercial operation
ACTIVITY

an activity that is intended to achieve a particular purpose:

a joint operation by French and Spanish police
an operation to smuggle drugs into Britain
in operation

If a machine or system is in operation, it is working or being used:

The new rail link is now in operation.
Most of the machines are now back in operation.

(Definition of “operation” from the Cambridge Learner’s Dictionary © Cambridge University Press)