Noun
shadow mask (plural shadow masks)
(television) A plate punched with tiny holes that separate the coloured phosphors in the layer behind the front glass of the screen. Three electron guns at the back of the screen sweep across the mask, with the beams only reaching the screen if they pass through the holes.
Firstly, for correct color rendering it is necessary that regardless of where the beams are deflected on the screen, all three hit the same spot (and nominally pass through the same hole or slot) on the shadow mask. Source: Internet
However, an excessively strong magnetic field, whether alternating or constant, may mechanically deform (bend) the shadow mask, causing a permanent color distortion on the display which looks very similar to a magnetization effect. Source: Internet
While CRT displays use red-green-blue-masked phosphor areas, dictated by a mesh grid called the shadow mask, it would require a difficult calibration step to be aligned with the displayed pixel raster, and so CRTs do not currently use subpixel rendering. Source: Internet
Therefore, it is important that the shadow mask is unmagnetized. Source: Internet