| Abbreviation | Definition |
|---|---|
| MR | Mountain Rider |
| MRA | Motorcycle Roadracing Association |
| MRC | Minuteman Racing Club |
| MRCA | Mississippi River Canoe Adventure |
| MRD | Manitou Racing Development |
| MRH | Men's Right Handed |
| MRMSA | Mystic River Mudhead Sailing Association |
| MRO | Motor Racing Outreach |
| MRP | Maui Raceway Park |
| MRP | Miyog Role Playing |
| MRRF | Motorcycle Road Racing Forums |
| MRW | Midwest Renegade Wrestling |
| MRW | MiniRaceWays Slot Car Speedway |
| MS | Men's Soccer |
| MS | Much Stamina |
| MSA | Montgomery Sports Association |
| MSA | Motor Sports Association |
| MSA | Motorsport South Africa |
| MSAC | Melbourne Sports Aquatic Centre |
| MSB | Mind, Spirit, and Body |