OST may refer to:
Music Original soundtrack, recorded sound accompanying a production such as a film O.S.T., an alias of electronic musician Chris Douglas O.S.T. (album), by the People Under the Stairs
Science and technology Object Storage Target in computing, used by the Lustre file system an others Oligosaccharyltransferase, an enzyme Open-space technology, for organising meetings Open Systems Theory, a form of sociotechnical systems pioneered by Fred Emery Orbit stabiliser theorem in mathematics Offline Storage Table, a Microsoft file format OST Family (organic solute transporter) of genes Origins Space Telescope, a space telescope mission Open Source Threat, any software demonstrating a device vulnerability that is open-source
Organizations Office of Science and Technology, a British government agency Office of Secure Transportation, a US government agency Order of the Solar Temple, French esoteric cult Organisation Socialiste des Travailleurs, the Socialist Workers Organisation of Senegal Outer Space Treaty, a treaty regulating international law in outer space.
Places Ostend–Bruges International Airport, Belgium, IATA code Old Spanish Trail (auto trail) East Germany, as with the name in german Ostdeutschland
Other uses Ost (game), a 1986 board game Ost (surname)