OP explained

OP or Op may refer to:

Arts and entertainment

One Piece, a 1997 Japanese manga and anime
OP, an abbreviated term for opening theme songs in anime
Opposite prompt, a stage right prompt corner on a theatre stage
Optimus Prime, a character from the Transformers franchise
Op., short for opus number, used to denote one work of musical composition from many
Original pronunciation, the phonology of Early Modern English, as used in William Shakespeare's time, specifically when used to perform his works in modern times.
Out of print, a status of a book title at a publishing house

Operational planning, the process of planning short term measures in a company
OP Financial Group, a Finnish company
Oborový podnik ("specialized business"), a bygone Czechoslovak state designation for a business entity
Ocean Pacific, a retail clothing company
Oratory Preparatory School, in New Jersey, United States
Dominican Order (Latin: Ordo Praedicatorum||links=no), a Catholic religious order
Odisha Police, police patrol in Odisha, India
Publications Office of the European Union, interinstitutional body of the European Union

Original post (or poster), the opening entry (or author thereof) in a thread or discussion in an internet forum
Overpowered (game balance), in video games, when a particular aspect or character is lacking game balance

Observation post, a position from which soldiers can watch enemy movements
Old Pauline, an ex-pupil of St Paul's School, London
Old Peterite, a former pupil of St Peter's School, York
Orange Pekoe, a grade of black tea
Organophosphate, the general name for esters of phosphoric acid
Overall Position, the grade appointed to Queensland high-school graduates
O.P. Anderson, a Swedish spirit of the aquavit type
Opportunity point, a tennis term for an opportunity to potentially break serve when the score is 15–30