| Abbreviation | Definition |
|---|---|
| MSM | Missouri State Militia |
| MSMA | Mutual Security Membership Application |
| MSMR | Military Spouse Managed Review |
| MSN | Message Sequence Number |
| MSN | Mission |
| MSN | Mission Starts Now |
| MSNAP | Merchant Ship Naval Augmentation Program |
| MSNF | Multiple System Networking Facility |
| MSNG | Marine Strategy Navigation Group |
| MSNN | Military Special Needs Network |
| MSO | Map Support Office |
| MSO | Maritime Security Operations |
| MSO | Medical Stability Operations |
| MSO | Medical Support Officer |
| MSO | Military Service Obligation |
| MSO | Military Source Operation |
| MSO | Military Strategic Objective |
| MSO | Military Support Operations |
| MSO | MILSATCOM (MILitary SATellite COMunications) Systems Organization |
| MSO | Mobilization Staff Officer |