| Abbreviation | Definition |
|---|---|
| MAR | Mississippi-Atchafalaya River |
| MARAD | Maritime Administration |
| MARC | MAchine-Readable Cataloguing |
| MARC | Milton Area Racing Circuit |
| MARD | Marine Assessment Research Division |
| MARIC | Marine Resources Information Center |
| MARMAP | Marine Resources Monitoring, Assessment and Prediction Program |
| MAS | Mobile Atmospheric Spectrometer |
| MASC | Mountain Administrative Support Center |
| MASTS | Marine Alliance for Science and Technology for Scotland |
| MB | Marine Board |
| MBA | Marine Biological Association |
| MBBW | Massachusetts Bay Bottom Water |
| MBCS | Marine Biology Case Study |
| MBDA | Minority Business Development Agency |
| MBE | Marine Bloom Experiment |
| MBHS | Member British Hydrographicological Society |
| MBL | Marine Biological Laboratory |
| MBL | Marine Boundary Layer |
| MBNMS | Monterey Bay National Marine Sanctuary |