(computing) An instruction or operation that has no effect; a null operation.

(LGBT, of a transgender or transsexual person) Having chosen not to undergo sex reassignment surgery.

(LGBT) A transgender or transsexual person who has chosen not to undergo sex reassignment surgery.

(informal) Clipping of operation. / (informal) An amateur radio operator. / (Internet) An operator on IRC, who can moderate the chat channel, ban users, etc.

(transitive, Internet) To promote (an IRC user) to an operator.

(Internet slang) Alternative letter-case form of OP (“original post, original poster”).

(slang, among criminal gangs) Alternative form of opp (“opponent; opposition”).

(Australia, informal, transitive) To buy (something) from an op shop. / (Australia, informal, intransitive) To shop at op shops.

(music, abbreviation) Opus. / (abbreviation) Operation. / (abbreviation) Operator. / (abbreviation) Operative. / (abbreviation) A detective. / An operator's license, usually ops

(Cornwall) alley or narrow passage e.g. Tonkin's Ope