Fos
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, an oncogene
FosB, an 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