OP, O.P., or Op may refer to any of the following:

  • Observation post, a position from which soldiers can watch enemy movements
  • Ocean Pacific, a retail company based in California, United States
  • Orange pekoe, a grade of black teas
  • Ordo Praedicatorum, a Catholic religious order
  • Operating profit, a measure of business profitability
  • Out of print, a status of a book title at a publishing house
  • Op, or grow-op, a marijuana growing operation
  • Open pollination
  • Operator (mathematics), a mapping from one vector space or module to another
  • Op (statistics), a symbol used in probability mathematics
  • Octagonal prism, a prism formed by square sides and two regular octagon caps
  • Op art, a style of visual art that makes use of optical illusions
  • Op-ed, a newspaper opinion piece of a writer unaffiliated with the editorial board
  • Opposite Prompt, stage right on a theatre stage
  • Op., an abbreviation for Opus number, used to denote one work of musical composition from many
  • Optimus Prime (Transformers), a character from the Transformers franchise
  • One Piece, a Japanese manga and anime
  • A shortening for opening credits, especially in anime fandom
Internet and gaming
  • Original post or original poster, the first post or person to post on a topic in an online forum
  • Overpowered, in video games, noting that a particular aspect or character is unbalanced and thereby too strong
  • An Internet Relay Chat operator
  • Oratory Preparatory School, a Catholic preparatory day school for boys in New Jersey, United States
  • Overall Position, the grade appointed to Queensland high-school graduates
  • Old Persean, an ex-pupil of The Perse School, Cambridge, England
  • Old Pauline, an ex-pupil of St Paul's School, London
  • Old Pangbournian, an ex pupil of Pangbourne College
  • Oak Park, Illinois
  • Oakland Park, Florida
  • Orchard Park, New York
  • Overland Park, Kansas
  • Ohio Penitentiary, a now-demolished prison
Science and medicine
  • The oropharyngeal airway, leading from the mouth to the pharynx
  • Organophosphate, the general name for esters of phosphoric acid
  • Osteitis pubis, a medical condition which is prevalent among players of Australian rules football
  • Osteoporosis, a degenerative disease of the bones
  • A surgical operation