| Abbreviation | Definition |
|---|---|
| MARA | Migration Agents Registration Authority |
| MARTA | Metro Area Rapid Transit Authority |
| MARTA | Metro Atlanta Rapid Transit Authority |
| MASADA | Movement to Arm Skipley Against Dictatorial Authority |
| MASE | Mandate Authority Strategy and Execution |
| MAWA | Meadville Area Water Authority |
| MBPA | Miami Beach Projection Authority |
| MBTA | Mass Bay Transit Authority |
| MBTA | Metropolitan Boston Transit Authority |
| MBTA | Mr Bakers Transportation Authority |
| MCAA | MONGOLIA Civil Aviation Authority |
| MCCA | Massachusetts Convention Center Authority |
| MCIA | Mauritius Cane Industry Authority |
| MCTA | Murray Calloway Transit Authority |
| MDBA | Murray Darling Basin Authority |
| MDBA | Murray-Darling Basin Authority |
| MDBA | MurrayDarling Basin Authority's |
| MDBA | Murray–Darling Basin Authority's |
| MDP | Market Data Processor |
| MECA | Metropolitan Entertainment Convention Authority |