| Abbreviation | Definition |
|---|---|
| MARA | Maine Alpine Racing Association |
| MARA | Mt Ashland Racing Association |
| MBHR | Mont Blanc Historique Racing |
| MBRA | Maritime Barrel Racing Association |
| MBRA | Michigan Bicycle Racing Association |
| MBRA | Midwest Barrel Racing Association |
| MBRA | Montana Bicycle Racing Association |
| MBWR | Mercedes Benz World Racing |
| MCR | Matchless Crown Racing |
| MCR | Mona City Raceway |
| MCRA | Michigan Canoe Racing Association |
| MCRA | Midwest Cafe Racing Association |
| MDR | Maiden Dirt Route |
| MDR | Mojave Desert Racing |
| MDR | Mojave Desert Racing, Incorporated |
| MDRA | Malta Drag Racing Association |
| MDRA | Midwest Drag Racers Association |
| MDRA | Motorcycle Drag Racing Association |
| MENCS | Monster Energy NASCAR Cup Series |
| MENTOR | Minorities Empowered Nationally Through Organized Racing |