PIXEL: a minute area of illumination on a display screen, one of many form which an images is composed.
MEGAPIXEL: a unit of graphic resolution equivalent to one million or (strictly) 1,048,576 pixels.
COLOR DEPTH: number of bits used to indicate the color of a single pixel, in a bit mapped image or video dram buffer or number of bits used for each color component of a single pixel.
BIT and BYTE: amount of computer memory are often expressed in terms of mega bytes or gigabytes