An N-type semiconductor is a type of material used in solar cells.

The MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) is a "first of its kind" design project of a nuclear reactor coupled to a proton accelerator (a so-called Accelerator-driven system (ADS)).

Municipal solid waste can be used to generate energy.

In solar cell research, carrier multiplication is the phenomenon wherein the absorption of a single photon leads to the excitation of multiple electrons from the valence band to conduction band.

Multiphase flow is the simultaneous flow of materials with two or more thermodynamic phases.

A multimeter is a measuring instrument that can measure multiple electrical properties.

In the physical sciences, a multilayer or stratified medium is a stack of different thin films.

Multi-junction solar cells are solar cells with multiple p–n junctions made of different semiconductor materials. Each material's p-n junction will produce electric current in response to different wavelengths of light.

Power plants that utilise more than one fuel source.

Also known as epicyclic gear train consists of two gears mounted so that the center of one gear revolves around the center of the other used in wind turbines.

Mixed oxide fuel, commonly referred to as MOX fuel, is nuclear fuel that contains more than one oxide of fissile material, usually consisting of plutonium blended with natural uranium, reprocessed uranium, or depleted uranium.

A motor–generator (an M–G set) is a device for converting electrical power to another form.

A motor soft starter is a device used with AC electrical motors to temporarily reduce the load and torque in the powertrain and electric current surge of the motor during start-up.

Moonlight consists of mostly sunlight reflected from the parts of the Moon's surface where the Sun's light strikes.

The Montreal Protocol on Substances that Deplete the Ozone Layer, also known simply as the Montreal Protocol, is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances that are responsible for ozone depletion.

A type of steam generator consisting of a single tube, usually in a multi-layer spiral, that forms a once-through steam generator.

A freestanding type of tower that is essentially a tube, often tapered in wind turbines.

A single, generally large-diameter, foundation structural element to support all the loads (weight, wind, etc.) of a large above-surface structure used for offshore wind turbines installations.

Momentum is the product of the mass and velocity of an object.

The moment of inertia, of a rigid body is a quantity that determines the torque needed for a desired angular acceleration about a rotational axis.