OS, O.S., Os, O's, or os may refer to:
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Austrian Airlines (IATA designator) (based on the original name of Österreichische Luftverkehrs AG)
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O.S. (Old Stonyhurst), a notation for alumni of the ancient Jesuit public school, Stonyhurst College
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O.S. Engines, a Japanese manufacturer of model aircraft engines
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Ocean Science, an oceanographic journal published by the European Geosciences Union
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Oculus sinister, meaning "left eye" in eyeglass prescriptions
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Ohtahara syndrome, a brain disorder
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Old Style date (O.S.), indicating the Julian Calendar, as opposed to "N.S." indicating from the Gregorian Calendar
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On-sight climbing, the ascent of a rock climbing route on the first attempt, with no falls, without prior knowledge of its specifics beyond its difficulty rating and number of protection points
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Open source, a software development model
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Operating system, a software that manages the hardware and software of a computer
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Order of Santiago, Spanish order dedicated to St James the Greater
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Ordinary Seaman, an unlicensed member of the deck department of a merchant ship
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Ordnance Sergeant, an enlisted rank in the U.S. and Confederate armies during the American Civil War era
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Ordnance Survey, the national mapping agency for Great Britain
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Ossetic language (ISO 639-1 abbreviation)
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Outlaw Star, a manga and anime series
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os, a mouth or external opening (from the Latin), also ostium. In particular:
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Ōs, in Old English denoting a god in Anglo-Saxon paganism, related to æsir
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Ōs (ᚩ), a rune of the Anglo-Saxon fuþorc
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Os, Hedmark, a municipality in Norway
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Os, Hordaland, a municipality in Norway
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Os, Østfold, a parish in Norway
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Os du Randt (born 1972), South African rugby player
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"Os", an episode of the television show Fringe
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Os Guinness (born 1941), English author and social critic
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Oś, Kluczbork County, Poland
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Osiedle, a name for a housing estate in Poland
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Osmium, a chemical element whose symbol is "Os"
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Baltimore Orioles
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Leyton Orient
See also
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Object sexuality, sexual attraction to inanimate objects
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Oral sex, sexual activity involving the stimulation of the genitalia of a sex partner by the use of the mouth, tongue, teeth or throat
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OutSystems, multinational software company which operates in the agile software development market
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Per os, a medical term for ingestion by mouth
