Cathode Ray Tube.
The technical name for a picture tube or scanning tube in a flying spot telecine. An electron beam is generated, accelerated, and made to strike a phosphor coating on the inside of an evacuated glass enclosure. The phosphor glows as a result of the energy imparted by the beam. By precisely controlling the position and intensity of the electron beam, meaningful patterns are made to appear in the phosphor and are visible through the glass.