The os is the external orifice of the uterus; it is the opening at the tip of the cervix which separates the uterus from the vagina.

Os may also refer to:

• Os, Hedmark, a municipality in Norway
• Os, Hordaland, a municipality in Norway
• Os, Østfold, a parish in Norway
• ?s, in Old English denoting a god in Anglo-Saxon paganism
• Osmium, a chemical element whose symbol is "Os"
• the Ossetic language (ISO 639-1)
• Os, the French word for "bone"
• Os Guinness (1941-), English author and social critic
• Os du Randt (1972-), South African rugby player

OS may refer to:

• Oculus Sinister (OS)-Latin for left eye- used commonly by physicians and pharmacists
• Open Source software
• Operating system, the software that manages the hardware and software of a computer
• Ogawa Seiki (aka O.S. Engine or O.S.), a Japanese manufacturer of model airplane engines
• Ordnance Survey (OS), the national mapping agency for Great Britain
• Open Seat, (aka Open Sabadell Atlantico or OS), a tennis tournament in Barcelona, Spain
• Old Style (OS), a term used in English language historical studies to indicate that a date conforms to the Julian calendar
• The IATA designator for Austrian Airlines
• Outlaw Star,a show that show that on Toonami,Fuji TV,and Adult Swim. The show had 26 episodes. This is the nickname of the show.
• On Sight - climbing ascent style

ca:Os (desambiguació) cs:OS de:OS es:Os eo:Os fr:OS ko:OS it:OS nl:OS ja:OS no:Os nn:Os pl:Os pt:OS ksh:OS (Watt ?ßß datt?) sk:Os sl:OS fi:Os sv:Os zh:OS