| Acronym | Definition |
|---|
| FOS | Factory Outlet Store (retail) |
| FOS | Festival of Speed |
| FOS | Financial Ombudsman Service (UK) |
| FOS | Fachoberschule (German school type) |
| FOS | Fortress of Solitude |
| FOS | Four of Spades (band) |
| FOS | Friends of Scouting |
| FOS | Family of Services (US FEMA) |
| FOS | Fructo-Oligosaccharides (nutrional supplement) |
| FOS | Faculty of Science (various universities) |
| FOS | Focus on Standards |
| FOS | File Output Stream |
| FOS | Free Online Scholarship |
| FOS | Failover Services |
| FOS | Family of Service |
| FOS | Fedora Operating System |
| FOS | Field of Search (sensor management systems) |
| FOS | Foreign Owned Subsidiaries |
| FOS | Freedom of the Seas (Royal Caribbean cruise ship) |
| FOS | Français sur Objectifs Spécifiques (French: French for Specific Purposes) |
| FOS | Field of Study |
| FOS | First Order Statistics |
| FOS | Field Office Supervisor (various organizations) |
| FOS | First on Stage |
| FOS | Fundamental Operating System |
| FOS | Factor Of Safety |
| FOS | Family of Systems |
| FOS | From Outer Space |
| FOS | Figure of Speech |
| FOS | Faint Object Spectrograph |
| FOS | Family of Spiders |
| FOS | free/open source |
| FOS | Florida Ornithological Society |
| FOS | Fiber Optic Splicing |
| FOS | Feat of Strength |
| FOS | Free Online Scholarship (newsletter) |
| FOS | French Onion Soup |
| FOS | Fructooligosacaridos |
| FOS | Flight Operations Support (various organizations) |
| FOS | Free Alongside Ship |
| FOS | Free Overnight Shipping |
| FOS | Federatie voor Open Scoutisme (Dutch: Federation for Open Scouting; Belgium) |
| FOS | Fiber Optic Sensor |
| FOS | Folks on Spokes (bicycle club) |
| FOS | Federation of Workers Trade Unions (Haiti) |
| FOS | Friend of the Sea (Sustainable Seafood) |
| FOS | Florida Orthopaedic Society |
| FOS | Field Operations Supervisor (Census) |
| FOS | Foundations of Science (journal; course) |
| FOS | Family of Schools |
| FOS | Forward Operating Site (US military) |
| FOS | First of Season (birding) |
| FOS | Federal Operations Support (US FEMA) |
| FOS | Fabric Operating System (Brocade) |
| FOS | Finnish Optical Society |
| FOS | Fellowship of the Sun (fictitious religious organization; True Blood; TV show) |
| FOS | Flight Operations System |
| FOS | Fabrique d'Outillage de Saint-Étienne (French: Tools Factory of Saint-Étienne; Saint-Étienne, France) |
| FOS | Finkel-Biskis-Jinkins murine Osteogenicsarcoma (cancer research) |
| FOS | Fuel Oil Supply |
| FOS | Front Office System (software) |
| FOS | Freedom of Services (EU) |
| FOS | Faint Object Spectrometer |
| FOS | Free On Steamer |
| FOS | Finger of Suspicion |
| FOS | Fish Odor Syndrome |
| FOS | Flight Operation Segment |
| FOS | Full of Stool (medical slang) |
| FOS | Follow On Support |
| FOS | Full of Stuff (polite form) |
| FOS | Florida Oceanographic Society |
| FOS | Full Operational Status |
| FOS | Fall Of Shot |
| FOS | Frinton on Sea (Essex, UK) |
| FOS | First on Scene (first aid) |
| FOS | Foot of Slope (change of gradient) |
| FOS | Focus on Solving |
| FOS | Friends of Science Society (Calgary, AB, Canada) |
| FOS | Followers of Set (roleplaying) |
| FOS | Fire Of Savannas |
| FOS | Freedom of Speech, Inc |
| FOS | Feature of Size (geometric dimensioning) |
| FOS | Feet on Street (India) |
| FOS | Fuel Operator Station |
| FOS | Found On Shelf |
| FOS | Follow on Sustainment |
| FOS | Follow On Spares |
| FOS | Flight Operations Software |
| FOS | Failure of Selection (US DoD) |
| FOS | Fuel Oil Spill |
| FOS | Frosts of Sweden (knife manufacturer) |
| FOS | Father Over Shoulder |
| FOS | Full Operating System |
| FOS | Fast Optical Shutter |
| FOS | Feasibility of Support |
| FOS | Fit or Split |
| FOS | Forward Observer Software/System |
| FOS | Fleet Ordnance Support |
| FOS | Funky Old Soul |
| FOS | Follow On Ship |
| FOS | Financial Operations Supervisor |
| FOS | Friends of Suai |
| FOS | Front Offside (vehicular collision reports) |
| FOS | former owner's stamp (used books) |
| FOS | Fellowship of the Services |
| FOS | Field Operation Service |
| FOS | Functional Operational Specification |