RSO
- Bavarian Radio Symphony Orchestra
- Danish National Symphony Orchestra
- Finnish Radio Symphony Orchestra
- Frankfurt Radio Symphony Orchestra
- Lockheed SR-71 Blackbird
- North German Radio Symphony Orchestra
- Order of the Sword
- Orianthi
- RSO Records
- Radiation Safety Officer
- Radschlepper Ost
- Railway Sub Office
- Range safety
- Raupenschlepper, Ost
- Reactive Search Optimization
- Red Star OS
- Regional Security Office
- Regional Security Officer
- Registered sex offender
- Resident Space Object
- Revised Statutes of Ontario
- Richardson Symphony Orchestra
- Richie Sambora
- Rick Simpson Oil
- Roanoke Symphony Orchestra
- Rogers Sportsnet Ontario
- Rohingya Solidarity Organisation
- South Ossetia
- Stuttgart Radio Symphony Orchestra
- Swedish Radio Symphony Orchestra
- Vienna Radio Symphony Orchestra