C.R.T.

C.R.T. is the abbreviation for cathode ray tube.  It is used in technological devices such as computer monitors and television screens.  It is used to move an electric beam back and forth across the display screen.   Every time the electric beam passes across the screen, phospor dots in a glass tube are lit and flow around the glass (the screen).

The beam draws lines from top to bottom on the screen and creates all the images that you see.  When people refer to computer monitors, they sometimes call it a C.R.T.  New televisions, such as plasma screens, LCDs, or anything that is non-projection type, does not contain a cathode ray tube.