FOS or Fos may refer to:
Arts and entertainment Fos (EP), by Elena Paparizou Fortress of Solitude, fictional base of Superman
Food French onion soup, a dish Fructooligosaccharide, a sweetener
Government, law and military Financial Ombudsman Service, in the United Kingdom Financial Ombudsman Service (Australia) Forward Operating Site, in the U.S. military Freedom of speech, a human right Future Office System, Scottish prosecutors' case system
People Fos Williams (1922–2001), Australian-rules footballer Peter J. Fos (born 1949), American academic administrator
Places Fos, Haute-Garonne, France Fos, Hérault, France Fos-sur-Mer, Bouches-du-Rhône, France Marseille-Fos Port, France Forrest Airport, Western Australian refuelling airfield, IATA code FOS French Overseas Territories, UNDP country code, see Overseas territory (France)
Science and technology Fabric OS, in networking Factor of safety, in engineering Feature-oriented scanning, in microscopy Faint Object Spectrograph, on the Hubble Space Telescope Fields of Science and Technology, a classification for academic statistics Flowers of sulfur Flowers of sulfur tests
Molecular biology FOS-family transcription factors: c-Fos, a proto-oncogene FosB, a proto-oncogene ΔFosB, a truncated splice variant of FosB FOSL1, Fos-related antigen 1 FOSL2, Fos-related antigen 2
Other uses Florida Ornithological Society, United States FOS Open Scouting, a Belgian youth organisation Goodwood Festival of Speed, an English hill-climbing event