They mean De_Gauss which is something like to remove magnetism from a device. The term is usually used in reference to color monitors and other display devices that use a Cathode Ray Tube (CRT). These devices aim electrons onto the display screen by creating magnetic fields inside the CRT. External magnetic forces -- such as the earth's natural magnetism or a magnet placed close to the monitor -- can magnetize the shadow mask, causing distorted images and colors.

Obviously this doesnt happen on TFT screens, so its probably a power feed issue or the cells in that perticular region have died.