| Registered Student Organizations | Academic & Science |
| Recognized Student Organization | Academic & Science |
| Registered Student Organization | Academic & Science |
| Rochester Student Organization | Academic & Science |
| Rectified Skew Orthomorphic | Academic & Science |
| Recognized Student Organizations | Academic & Science |
| Round, Square, and Oval | Business |
| Roger & Sherry Olsen Livestock | Business |
| Retirement Services Officer | Business |
| RIMCO Support Office | Business |
| Robert Stigwood Organization | Business |
| Rockford Symphony Orchestra | Community |
| Roanoke Symphony | Community |
| Resident Services Office | Community |
| Regina Symphony Orchestra | Community |
| Roanoke Symphony Orchestra | Community |
| Regional Support Office | Community |
| Rapid Scan Operation | Computing |
| Remote Shared Object | Computing |
| Remote Spool Output | Computing |
| Remote Switch Operator | Computing |
| Radiation Service Officer | General |
| Radiographic safety officer | General |
| Radiation Service Organization | General |
| Robert Stigwood | General |
| Rick Simpson Oil | General |
| Recognized Service Organization | General |
| Regionalny System Ostrzegania | General |
| Regimental Supply Officer | General |
| Rough Stud Opening | General |
| Rainbow Service Organization | General |
| Radiation Safety Officers | General |
| Registered Service Organization | General |
| Recognized Security Organization | General |
| Rock Sh*t On | General |
| Ridiculously Showing Off | General |
| Road Safety Officer | General |
| Road Safety Observatory | General |
| Rally Sport Omologato | General |
| Rapid Specification Option | General |
| Road Safety Organization | General |
| Rear Seat Occupancy Alarm | General |
| Rally Sport Ontario | General |
| Retirement Services Office | General |
| Recognized Service Organizations | General |
| Rent Stabilization Ordinance | General |
| Robert Stigwood Organisation | General |
| Rock Solid Organization | General |
| Refinery Safety Overview | General |
| Range Safety Officer | Governmental |
| Registered Safety Officer | Governmental |
| Reconnaissance Systems Officer | Governmental |
| Reconnaissance and Surveillance Operation | Governmental |
| Regional Support Organization | Governmental |
| Radiological Safety Office | Governmental |
| Radiation Safety Officer | Governmental |
| Regional Security Officer | Governmental |
| Rock S*** On | Internet |
| Resident Surgical Officer | Medical |
| Right superior oblique | Medical |
| Regional Sales Office | Regional |
| Regional Sub Office | Regional |
| Revised Statutes of Ontario | Regional |
| Reality Sports Online | Sports |
