A beam of electrons which, when striking a phosphor-coated surface (such as the back of a television or computer screen), creates light-emitting dots or pixels. The motion of the ray across and down the screen is controlled by a deflection unit. In a monochrome monitor, there is a single cathode ray. In an RGB monitor, there are three (a red, a green, and a blue). A cathode ray is emitted by a device known as an electron gun.