Picture Element
The elements of a raster, arranged in rows and columns, each representing the color value of an image, at that point.
Most images displayed on a computer are comprised of pixels. Analog television images are not. Television images are represented by continuously varying analog wave forms.
Digital video/television images have rectangular pixels! This is an artifact of the way analog video is scanned onto the screen. It's an ugly little fact, but one that graphics artists that work in TV have to deal with.