1. The action of intervening; interfering in some course of events.
2. (US, law) A legal motion through which a person or entity who has not been named as a party to a case seeks to have the court order that they be made a party.
3. An orchestrated attempt to convince somebody with an addiction or other psychological problem to seek professional help and/or change their behavior.
4. (medicine) An action taken or procedure performed; an operation.