A cathode-ray tube is a display device used in television sets and computer monitors. It is a kind of vacuum tube which contains one or more electron guns, electrostatic deflection plates and a phosphor target which is located at the back of the glass screen. A cathode for which the CRT got its name is a positive terminal at which electrons may enter.

In a computer monitor or in a television set, the entire front of the tube is being scanned systematically and rapidly in a fixed pattern which is called a raster. Images and color are produced by shooting and controlling the electron beams representing each additive color light (red, blue and green) using the video signal as the reference.

Modern CRT monitors use magnetic deflection to bend the electron beams. This is done by varying the magnetic field generated by coils which is driven by electronic circuits located along the neck of the tube.