MR. Halogen Bulbs

A multifaceted reflector (often abbreviated MR) light bulb is a reflector housing format for halogen as well as some LED and fluorescent lamps.
MR lamps were originally designed for use in slide projectors, but see use in residential lighting and retail lighting as well.
They are suited to applications that require directional lighting such as track lighting, recessed ceiling lights, desk lamps, pendant fixtures, landscape lighting, retail display lighting, and bicycle headlights.