Multi-faceted Reflector Lamp, the most popular of which is MR16. MR lamps surround a halogen capsule with a designed glass or metal reflector with many surfaces or facets. These compact lamps require a glass cover, either integral or with the fixture. Most MR lamps incorporate dichroic reflectors, which pass heat out the black of the lamp and reflect visible light forward in a cooler beam.

Reference: ©American Lighting Association