| M | Number of Antenna Elements or Beams in a Smart Antenna |
| M2PA | Message Transfer Protocol 2 Peer-to-Peer Adaptation |
| M2UA | Message Transfer Protocol 2-user Adaptation Layer |
| M3UA | Message Transfer Protocol 3-user Adaptation Layer |
| MA | Media Access Control |
| MAC | Media (Medium) Access Control |
| MADU | Multiwave Add/Drop Unit |
| MAN | Metropolitan Area Network |
| MANET | Mobile Ad Hoc Network |
| MAP | Mobile Applications Part |
| MAS | Multiple-Application Selection |
| MB | Megabyte |
| Mb | Megabit |
| MBAC | Measurement-Based Admission Control |
| MBE | Molecular Beam Epitaxy |
| MBGP | Multicast Border Gateway Protocol |
| MBMS | Multimedia Broadcast/Multicast Services |
| MBone | Multicast Backbone |
| Mbps | Megabits Per Second |
| MBWA | Mobile Broadband Wireless Access |
| MC | Multipoint Controller |
| MCC | Mobile Country Code |
| MCI | Multiplex Configuration Information |
| MCM | Multichip Module |
| MCMs | Multi-Chip Modules |
| MCS | Multipoint Communications Systems |
| MCU | Multipoint Control Unit |
| MDAC | Multiply Digital to Analog Converter |
| MDARS | Mobile Detection Assessment Response |
| MDF | Main Distribution Frame |
| MDK | Minimum Shift Keying |
| MDS | Multipoint Distribution Systems |
| MDSL | Multiple DSL |
| MDTP | Media Device Transport Protocol |
| MDU | Multiple Dwelling Unit |
| MEF | Metro Ethernet Forum |
| MEGACO | Media Gateway Control |
| MEMS | Micro-electromechanical Systems |
| MEO | Medium Earth Orbit |
| MESFET | Metal Schottky Field Effect Transistor |
| MExE | Mobile Execution Environment |
| MFJ | Modified Final Judgment |
| MG | Media Gateway |
| MGC | Media Gateway Controller |
| MGCP | Media Gateway Control Protocol |
| MHz | Megahertz |
| MIB | Management Information Base |
| MID | Molded Interconnect Device |
| MII | Media Independent Interface |
| MIM | Metal Insulator Metal |
| MIME | Multipurpose Internet Mail Extensions |
| MIMO | Multiple Input Multiple Output |
| MIMOSA | Micro Systems for Mobile Services & Applications |
| MIN | Mobile Identification Number |
| MIPS | Millions of Instructions Per Second |
| MIS | Management Information System |
| MITI | Ministry of International Trade and Industry (Japan) |
| MLC | Multi Layer Products |
| MLT | Mechanized Loop Testing |
| MM | Mobility Management |
| MMAC | Million Multiply Accumulate Operations |
| MMACPC | Multimedia Access Communication Systems Promotional Council |
| MMAS | Material Management and Accounting Systems |
| MMDS | Multichannel Multipoint Distribution Service |
| MMI | Monolithic Microwave Integrated Circuit |
| MMIC | Monolithic Microwave Integrated Circuit |
| MMPP | Markov-Modulated Poisson Process |
| MMS | Multi-Media Messaging |
| MMusic | Multiparty Multimedia Session Control [working group] |
| MMW | Millimeter Wave |
| MNC | Mobile Network Code |
| MOM | Message-oriented Middleware |
| MOMO | Multiple In, Multiple Out |
| MON | Metropolitan Optical Network |
| MOP | Method of Procedure |
| MOS | Mean Opinion Score |
| MOSFP | Multicast Open Shortest Path First |
| MOT | Multimedia Object Transfer |
| MOTS | Military Off The Shelf |
| MoU | Memorandum of understanding |
| MOU | Minutes of Use |
| MP3 | Moving Picture Experts Group Layer 3 Audio |
| MPC | Mobile Positioning Center |
| MPEG | Motion Picture Expert Group |
| MPI | Message Passing Interface |
| MPLambdaS | Multiprotocol Lambda Switching |
| MPLS | Multiprotocol Label Switching |
| MPM | Mobile Presence Management |
| MPOA | Multiprotocol Over ATM |
| MPOE | Multiple Point of Entry |
| MPOP | Metropolitan Point of Presence |
| MPP | Massively Parallel Processor |
| MPx | MPEG-Layer x |
| MRC | Monthly Recurring Charge |
| MRD | Marketing Requirements Document |
| MRF | Media Resource Function |
| MRR | Medium Range Radar |
| MRS | Menu Routing System |
| MRSP | Mobile Radio Service Provider |
| ms | millisecond |
| MS/s | Million Samples Per Second |
| MSA | Metropolitan Statistical Area |
| MSC | Mobile Switching Center |
| MSC | Main Service Channel |
| MSF | Multiservice Switch Forum |
| MSIN | Mobile Station Identification Number |
| MSL | Moisture Sensitivity Level |
| MSNAP | Multiple Services Network Access Point |
| MSO | Multiple-System Operator |
| MSP | Management Service Provider |
| MSPS | Million Samples Per Second |
| MSS | Mobile Satellite Service |
| MSS | Multiple-Services Switching System |
| MSSP | Mobile Satellite Service Provider |
| MTA | Major Trading Area |
| MTBF | Mean Time between Failures |
| MTP-[x] | Message Transfer Part-[x] |
| MTSO | Mobile Telephone Switching Office |
| MTTF | Mean Time to Failure |
| MTTR | Mean Time To Repair |
| MTTS | Microwave Telephony Telegraphy and Satellite |
| MTU | Multiple-Tenant Unite |
| MUSO | Mobile User Objective System |
| MUX | MultiPlex Communications Transmissions |
| MUX/DEMUX | Multiplexer/Demultiplexer |
| MVL | Multiple Virtual Line |
| MVNA | Modulated Vector Network Analysis |
| MW | Microwave |
| MWIF | Mobile Wireless Internet Forum |
| MZI | Mach-Zender Interferometer |