| Abbreviation | Definition |
|---|---|
| MMCX | M&M Chemical Products (TransMatrix) |
| MMCX | TransMatrix Incorporated |
| MMID | Maryland Midland Railway |
| MMID | Maryland Midland Railway Incorporated |
| MMMU | Fesco Pacific Lines |
| MMMX | Minnesota Mining and Manufacturing - 3M |
| MMMX | Minnesota Mining and Manufacturing (3M) |
| MMRA | Melbourne Metro Rail Authority |
| MMRR | Mid- Michigan Railroad Incorporated |
| MMRR | Mid-Michigan Railroad |
| MMRX | Double M Ranch Enterprises |
| MMSX | Blue Circle |
| MMTS | Multi-Modal Transport System |
| MMXZ | Murphy Motor Express |
| MMXZ | Murphy Motor Express Inc |
| MNA | Missouri and Northern Arkansas Railroad |
| MNA | Missouri and Northern Arkansas Railroad Company |
| MNAX | C and S Directional Boring |
| MNBR | M and B Railroad |
| MNBR | M and B Railroad L.L.C. |