OS

OS, O.S., Os, O's, or os may refer to:

• Operating system, collection of software that manages computer hardware and software resources
• Open source (disambiguation)
• OpenStack, a software platform for cloud computing

• os or ostium, a mouth or mouth-like opening
  • per os, meaning "ingestion by mouth"
  • external os, the external orifice of the uterus
  • internal os, the internal orifice of the uterus
  • os or ostium, the opening of a coronary artery
• O.S. or OS, oculus sinister, meaning "left eye" in general ophthalmologic or optometric usage, particularly in eyeglass prescriptions (deprecated abbreviation)
• Ohtahara syndrome, a brain disorder
• Overall survival rate, a cancer survival statistic
• Oneiroid syndrome, a dreamlike fantastic delusional state

• Alexander Os (born 1980), a Norwegian biathlete
• Os du Randt (born 1972), a South African rugby player
• Os Guinness (born 1941), an English author and social critic
• For people named van Os see Van Os

• Esker, also os, a long, winding ridge of sand and gravel in (formerly) glaciated regions
• Ordnance Survey, national mapping agency of Great Britain
• Austrian Airlines (IATA code OS based on its original name: Österreichische Luftverkehrs AG)
• O.S. Engines, a Japanese manufacturer of model aircraft engines

• Ohio State Buckeyes, a group of collegiate teams representing The Ohio State University
• Os TF, a sports club in Os, Norway
• On-sight climbing, an ascent of a rock climbing route on the first attempt
• Orioles, nicknamed "O's":
  • Baltimore Orioles, a Maryland baseball team
  • Charlotte Orioles, a North Carolina baseball team, renamed the Charlotte Knights in 1988
• Leyton Orient F.C., an English football (soccer) team nicknamed "O's"
• London Olympians, named 1995–2005 as London O's, an American football team based in Greenwich, London, England

• Ordinary seaman, an unlicensed member of the deck department of a merchant ship
• Ordnance sergeant, an enlisted rank in the U.S. and Confederate armies during the American Civil War era
• Old Shirburnian, used by alumni of Sherborne School
• Old Stonyhurst, used by alumni of Stonyhurst College
• O.S., Order of Santiago, a Spanish order dedicated to St James the Greater
• O.S., Order of Sikatuna, the national order of diplomatic merit of the Philippines

• Ōs (rune) (ᚩ), a rune of the Anglo-Saxon fuþorc
• Ossetic language (ISO 639-1 abbreviation OS)

• "O's", a name for breakfast cereal with O-shaped pieces, cereal similar to , e.g. Oreo O's, Krusty-O's, some kinds of Cheerios — seelist of breakfast cereals to find more
• SpaghettiOs, a brand of canned ring-shaped pasta in tomato sauce
• Newman-O's, cookies made by Newman's Own

• Ocean Science (journal), an oceanographic journal
• Osmium, symbol Os, a chemical element
• "Os" (Fringe), an episode (S3 E16 / #59) of the television show Fringe
• Old Style (O.S.) date, indicating use of an earlier calendar (in Anglophone countries, the Julian Calendar), as opposed to "N.S." (new style), usually indicating use of the Gregorian Calendar
• Ōs, an Old English word denoting a god in Anglo-Saxon paganism, related to æsir

• 0S (disambiguation)
• ÖS (disambiguation)
• Oz (disambiguation)
• O (disambiguation)
• X's and O's (disambiguation)
• Triple O's, a quick service brand associated with White Spot