(CRT, Cathode Ray Tube) A vacuum tube that produces light when energized by the electron beam generated inside the tube. A CRT has a heater element, cathode, and grids in the neck of the tube, making up the "gun". An electron beam is produced by the gun and is accelerated toward the front display surface of the tube. The display surface contains phosphors that light up when hit by the electron beam. The CRT is more commonly known as a picture tube.