Marine Surveyor: A person who conducts a survey of vessels to evaluate and report on their overall condition through assessment of their structure and the products and systems contained in them. Marine surveyors may have qualifying designations such as Yachts and Small Craft, Commercial Tug and Barge, Fishing Vessels, Engines, etc.
Mechanically Fastened Membrane: Generally used to describe membranes that have been attached at defined intervals to the substrate.
Meg: Prefix meaning one million times the root word. Example: 1 megohm = 1,000,000 ohms.
Membrane: A Flexible or semi-flexible roof covering or waterproofing whose primary function is to exclude water.
Membrane Base Flashing: See Flash Base
Meter: Unit of length measurement in the metric system; 1 meter is equal to 39.27 inches.
Mil: A unit of measure, one mil is equal to 0.001 inches, or 25.4 micrometers, often used to indicate the thickness of a roofing membrane.
Millimeter: A unit of measure equal to one thousandth (0.001) of a meter, or 0.03937 inches.
Mineral Granules: See Granule.
Mineral-Surfaced Roofing: Roofing materials whose surface or top layer consists of a granule-surfaced sheet.
Minimum Detectable Temperature Difference (MDTD): The smallest amount of temperature differential that can be detected by a thermal imaging system. MDTD is also known as thermal sensitivity.
Modified Bitumen: (1) A bitumen modified by including one or more polymers (e.g. a tactic polypropylene, styrene butadiene styrene, etc.); (2) Composite sheets consisting of a polymer modified bitumen often reinforced with various types of mats or films and sometimes surfaced with films, foils or mineral granules.

Moisture Meter Probe: An invasive (electrical resistance or galvanometric type) test that entails the insertion of a meter probe(s) into a material to indicate the presence of moisture. A moisture meter probe is used to make qualitative comparisons between different areas.
Moisture Scan: The use of a mechanical device (capacitance, infrared, or nuclear) to detect evidence of moisture within a roof assembly. (See Non-Destructive Testing.)
Motor: An electromagnetic device that converts electrical energy into mechanical energy.
