MSA
- 5-Methoxysalicylic acid
- China Maritime Safety Administration
- Freemasonry
- Indonesian Maritime Security Agency
- Japan Coast Guard
- Mackintosh School of Architecture
- Mad Science Alliance
- Magnuson-Stevens Act
- Maine Snowmobile Association
- Mainland Southeast Asia linguistic area
- Malay language
- Malaysia–Singapore Airlines
- Manchester School of Architecture
- Manchester Society of Architects
- Mannitol salt agar
- Mapping Services Agreement
- Market Square Arena
- Master of Accountancy
- Master of Advanced Studies in Sports Administration
- Master of Science in Administration
- Master service agreement
- Matthew Shepard Act
- Measurement system analysis
- Medical savings account
- Meritorious Service Award
- Message submission agent
- Metaphysical Society of America
- Methanesulfonic acid
- Metropolitan statistical area
- Micropolitan statistical area
- Microscopy Society of America
- Microservices
- Microsoft Access
- Microsoft account
- Middle States Association of Colleges and Schools
- Middle Stone Age
- Mine Safety Appliances
- Mineralogical Society of America
- Minimum safe altitude
- Minnesota Math and Science Academy
- Mississippi School of the Arts
- Missouri Scholars Academy
- Mobile Service Architecture
- Modern Sciences and Arts University
- Modern Standard Arabic
- Montessori School of Anderson
- Morphosyntactic alignment
- Motor Sports Association
- Motorway service area
- Movement for the Salvation of Azawad
- Multi-source agreement
- Multiple sequence alignment
- Multiple system atrophy
- Muskrat Dam Airport
- Muslim Students' Association
- Mutfak Sanatlari Akademisi
- Mutual Security Act
- Myanmar Space Agency
- Mycological Society of America
- Pakistan Maritime Security Agency
- Poste Air Cargo
- Tobacco Master Settlement Agreement
- U.S. and Japan Mutual Defense Assistance Agreement
- WAGR Msa class