| Acronym | Definition |
|---|
| FO | Fiber-Optic(s) |
| FO | Field Office |
| FO | Front Office |
| FO | Formatting Object (XSL) |
| FO | Foreign Office |
| FO | Face-Off (hockey) |
| FO | Faroe Islands |
| FO | First Order |
| FO | Follow On |
| FO | Foramen Ovale (neurology) |
| FO | Fallout (computer game) |
| FO | Foreign Object |
| FO | Formula One |
| FO | Fuel Oil |
| FO | Force Ouvrière (Workers Force) |
| FO | Force Ouvrière (French Labor Union) |
| FO | Forli (postcode, Italy) |
| FO | Freak Out |
| FO | Far Out |
| FO | First Officer |
| FO | Formosa (Argentina province, airline code) |
| FO | Fly-Over |
| FO | Factory Outlet (UK shopping channel) |
| FO | Fly Out (Baseball) |
| FO | Field Operations |
| FO | Finance Officer |
| FO | Fluid Ounce (unit of measurement) |
| FO | Fantasy Online (video game) |
| FO | Flight Operations |
| FO | Furnace Oil |
| FO | Forward Observer |
| FO | Flying Object |
| FO | Foldout |
| FO | Foul Out (baseball) |
| FO | Full Out (typography) |
| FO | Foreign Objects (band) |
| FO | Finished Object (crafts) |
| FO | Fitting Out |
| FO | Furka Oberalp (railway in the Alps) |
| FO | Flip Off |
| FO | Force Operations |
| FO | Foreign Service Officer |
| FO | Field Order |
| FO | Fail Operational |
| FO | Flag Officer (Royal Navy) |
| FO | Flying Officer (Royal Air Force & commonwealth countries) |
| FO | Flight Officer |
| FO | Fairly Oddparents (cartoon) |
| FO | Firm Offer |
| FO | Fiscal Officer |
| FO | Firm Order |
| FO | Forsvarets Overkommando (Norwegian) |
| FO | Fail Open |
| FO | Flake Off (polite form) |
| FO | Flight Order (US Navy) |
| FO | Flash Override |
| FO | Fourth Official (soccer) |
| FO | Facilities Office |
| FO | Fire Order |
| FO | Friendship Over |
| FO | Forced Outage (power industry) |
| FO | Forlì, Emilia (Italian province) |
| FO | Frequent Observation |
| FO | Farmowners (multiple line insurance policy covering farmowner's property and liability coverage) |
| FO | First Orbit |
| FO | First Orchestra (Plano, TX) |
| FO | Frosted Orange (drink) |
| FO | Focus Offset |
| FO | Flow Orifice |
| FO | Full Organ |
| FO | Federation Object |
| FO | Foreign Operations Administration |
| FO | Flight Object |
| FO | Fun Orb (game website) |
| FO | Fully Orthogonal |
| FO | Free Overside |
| FO | Fire & Observe |
| FO | Functional Orthosis |
| FO | Form Stroke (swimming) |
| FO | Finsbury Orthopaedics Ltd (UK) |