I was out for a birthday lunch today and a friend asked what a pixel is. After fumbling around for a good description, I figured I would put the more refined version here for you all to read.
The smallest part of the video monitor display is a tiny rectangular or square dot called a pixel. The word pixel is a combination of two common words, picture, and element. A pixel is best described as a relative, rather than discrete unit because the physical size of an individual pixel is determined by the monitor manufacturer. However, pixels can be measured. Pixel size is generally measured in millimeters (mm).
The particular color of a pixel is a combination of up to three main colors. I do not use the word primary colors because those are red blue and yellow and computers use red, green, and blue. Up to three bytes of data are used to identify an individual pixel with one byte (8-bits) used for each color. A true color, or 24-bit color display system, uses all three bytes at 24 bits per pixel (8-bits in a byte X 3 bytes), permitting more than 16 million different colors to be displayed (2 to the 24th power). However, most color display systems use only eight bits per pixel, which provides up to 256 different colors.
The quality of a display system depends on its resolution, or how many pixels the monitor can display, and how many bits are used to represent each pixel. Video Graphic Adapter (VGA) based computers can display up to 640 by 480 pixels, or about 300,000 pixels. Super Video Graphics Adapter (SVGA) based computers can display up to 1,024 by 768 pixels, or nearly 800,000 pixels.
I hope that explains the basics. Any questions?