Fresnel Light - a focusable spotlight used in film, television, and theater lighting, which can be adjusted via a knob on the back of the light from "spot" for a narrowly focused beam, to "flood" for a wider beam.  This type of focusable lighting instrument is called a Fresnel because it features a Fresnel Lens, a glass lens with concentric ripples that is visible on the front of the light, casting soft, even illumination across the light's beam.