| Abbreviation | Definition |
|---|---|
| MFMR | Maritime Federation of Model Railroaders |
| MG | Mobile and Gulf Railroad |
| MGA | Consolidated Rail Corporation |
| MGA | Monongahela Railway (Norfolk Southern Railway) |
| MGGU | Marcevaggi |
| MGGU | Marcevaggi, SP. A. |
| MGLEE | Metro Gold Line Eastside Extension (rail system; Los Angeles, CA) |
| MGLP | Mangolpuri, Delhi, railway station |
| MGMU | Mega Containers Sales |
| MGMX | J and J Partnership |
| MGNU | Seacube Container Leasing |
| MGRI | MG Rail |
| MGRI | MG Rail Incorporated |
| MGRS | Ferrocarriles Nacionales de Mexico |
| MGSX | Martin Gas Sales (CF Martin Sulphur) |
| MGSX | Martin Gas Sales Incorporated |
| MH | Mount Hood Railroad |
| MH | Mt. Hood Railroad Company |
| MHAX | U.S. Department of Interior-Bureau of Mines Helium Field Operations |
| MHAX | United States Department of the Interior Bureau of Mines Helium Field Operations |