| Acronym | Definition |
|---|
| OSA | Optical Society of America |
| OSA | Obstructive Sleep Apnea |
| OSA | Office of Student Affairs |
| OSA | Office of the State Auditor |
| OSA | Office of Special Affairs (Church of Scientology International) |
| OSA | Office of Substance Abuse |
| OSA | Optical Spectrum Analyzer |
| OSA | Open Service Access (3GPP) |
| OSA | Open Systems Architecture |
| OSA | Official Secrets Act |
| OSA | Open Service Architecture |
| OSA | Organizzazione degli Stati Americani |
| OSA | operational support airlift (US DoD) |
| OSA | Outstanding Service Award |
| OSA | Open Software Associates |
| OSA | Ordo Sancti Augustini (St Augustine Order) |
| OSA | Order of Saint Augustine |
| OSA | Overseas Subscribers Agents (lottery agent) |
| OSA | Office of the Secretary of the Army |
| OSA | Overseas Students' Association (University of Adelaide, Australia) |
| OSA | Operational Support Aircraft |
| OSA | Organization of Staff Analysts (New York, NY) |
| OSA | Optimal Shelf Availability |
| OSA | Organización Sionista Argentina |
| OSA | Optical Subassemblies (Palomar Technologies) |
| OSA | Opportunistic Spectrum Access |
| OSA | Om Svar Anhålles |
| OSA | Oberstabsarzt (German military) |
| OSA | Oscilloquartz SA (Switzerland) |
| OSA | Organizations and Strategies in Astronomy |
| OSA | Object Services Architecture |
| OSA | Otto Schulze Autometer |
| OSA | Open Solutions Architecture (Novell) |
| OSA | Orchid Society of Arizona (Phoenix, AZ) |
| OSA | Ordinis Sancti Augustini (of the order of St Augustine) |
| OSA | Old Stone Age (gaming forums) |
| OSA | Online Sexual Activity |
| OSA | Order of St Anne |
| OSA | Open Space Assessment |
| OSA | Open Security Architecture (Nortel) |
| OSA | Our Special Ale (Anchor Christmas Ale) |
| OSA | Office Solution Accelerator (Microsoft) |
| OSA | Oregon Society of Anesthesiologists |
| OSA | Opus Sanctorum Angelorum (Latin: Work of the Holy Angels; religious order) |
| OSA | Ocala Sportsman's Association, Inc (Florida, USA) |
| OSA | Old Stock Ale (North Coast Brewery) |
| OSA | Office of Space Acquisition |
| OSA | Office of the Space Architect |
| OSA | Operational Support Authority |
| OSA | Olympic Science Alliance |
| OSA | Officially Step Aside |
| OSA | Outfitting Supply Activity |
| OSA | Office of Safety Appraisals |
| OSA | Orbiter-based Station Avionics |
| OSA | Out of Station Allowance |
| OSA | Outfitting Support Activity |
| OSA | Hermits of St. Augustine, Augustinians (religious order) |
| OSA | Objective Switching Architecture |
| OSA | Operational Safety Analysis/Assessment |
| OSA | Operating System Account |
| OSA | Optic Stabilizer Assembly |
| OSA | OPLAN Supportability Analysis |
| OSA | Ontology Server for Archaeological Information Retrieval and Processing |
| OSA | observability subspace algorithm |
| OSA | On-Screen Analysis |
| OSA | Organización de Seguros Africanos (Spanish: African Insurance Organization) |
| OSA | Online Selling Association (Hutchinson, KS) |