screen burn-in

Screen burn-in, image burn-in, ghost image, or shadow image, is a permanent discoloration of areas on an electronic visual display such as a cathode-ray tube (CRT) or organic light-emitting diode (OLED) in a computer monitor or television set. It is caused by cumulative non-uniform use of the screen.
Newer liquid-crystal displays (LCDs) may suffer from a phenomenon called image persistence instead, which is not permanent.
One way to combat screen burn-in was the use of screensavers, which would move an image around to ensure that no one area of the screen remained illuminated for too long.

View More On Wikipedia.org