An abbreviation of “picture element” but so much more! Basically it’s a mathematical abstraction, not simply a “dot on the screen”, as one may mistakenly presume. Nor does it have a physically determinate size, since it’s size is dependent upon many factors, including screen resolution of the display device. This can become very metaphysical very quickly, but essentially as an abstraction that is processed electrically via “computer parts” (extreme layman’s terms) and represented on the display via RGB color values, pixels are in effect not “real” but simulations/representations of mathematically defined logical structures/units. Sounds like the matrix, doesn’t it???
More to it than this…trying to find papers/books that refer to this deeper view of pixels and will update shortly.