| Magnetic Field | The region within which a body or current experiences magnetic forces |
| Magnetic Flux | The rate of flow of magnetic energy across or through a surface (real or imaginary). |
| Magnetic Noise | Changes in the current level within a cable caused by an external magnetic field |
| MCM | One thousand circular Mils |
| Megarad | A unit for measuring radiation dosage. Equal to one million rads. |
| Megohm | One million ohms |
| Member | A group of insulated wires to be cabled with other stranded groups into multiple-membered cable |
| Messenger | The linear supporting member, usually a high strength steel wire, used as the supporting element of a suspended aerial cable. The messenger may be an integral part of the cable, or exterior to it. |
| Mho | The unit of conductivity. The reciprocal of an ohm. |
| MHz | Megahertz (one million cycles per second). |
| Microphonics | Noise in a system caused by mechanical vibrations |
| Microwave | A short (usually less than 30cm.) electrical wave |
| Mil | A unit used in measuring diameter of a wire or thickness of insulation over a conductor. One one thousandth of an inch (.001"). |
| Mis-Match | A termination having a different impedance than that for which a circuit or cable is designed |
| Modules of Elasticity | The ratio of stress to strain in an elastic material |
| Moisture Absorption | The amount of moisture, in percentage, that a material will absorb under special conditions |
| Moisture Resistance | The ability of a material to resist absorbing moisture from the air or when immersed in water |
| Monomer | The basic chemical unit used in building a polymer |
| MP | Designation of multi-purpose cable that meets Vertical Tray flame test |
| MPP | Designation of multi-purpose cable that meets Steiner Tunnel test |
| MPR | Designation of multi-purpose cable that meets Riser flame test |
| MTW | Thermoplastic insulated machine tool wire |
| Multiconductor | More than one conductor within a single cable complex |
| Mutual Capacitance | Capacitance between two conductors when all other conductors including ground are connected together and then regarded as an ignored ground |
| Mutual Inductance | The ratio of voltage induced in one conductor to the time rate of current change in the separate conductor causing this induction |
| Mylar | DuPont trademark for polyester material used in the form of a tape |
