| Abbreviation | Definition |
|---|---|
| MLB | Major Leauge Baseball |
| MLB | Maple Leaf Baseball |
| MLB | Marxist Leninist Baseball |
| MLB | Minor League Baseball |
| MLBAM | Major League Baseball Advanced Media |
| MLBP | Major League Baseball Properties |
| MLBPA | Major League Baseball Players Association |
| MLFB | Major League Fantasy Baseball |
| MLLB | McKinney Little League Baseball |
| MM | Marcus Madrid, baseball pitcher |
| MNBA | Mississauga North Baseball Association |
| MNBN | Modesto Nuts Baseball Network |
| MON | Montreal Expos |
| MSBL | Mens Senior Baseball League |
| MSBL | Mid Suburban Baseball League |
| MSBP | MIT Science of Baseball Program |
| MUBC | Melbourne University Baseball Club |
| MUFF | Error, in Baseball |
| MUSB | Mendon Upton Senior Baseball |
| MVR | Manager Visits Remaining |