FSO
- F.S.O.
- Fabryka Samochodów Osobowych
- Fairfax Symphony Orchestra
- Federal Protective Service (Russia)
- Federal Statistical Office (Switzerland)
- Film Symphony Orchestra
- Financial Secretary's Office
- Fire Support Officer
- Flag Service Organization
- Flash shared object
- Floating storage and offloading
- Foreign Service Officer
- Forest Section Officer
- Franklin County State Airport
- Frankston Symphony Orchestra
- Free-space optical communication
- Fulham Symphony Orchestra
- Subiaco railway station