CMYK

CMYK (cyan, magenta, yellow, key/black), or process color, is a  that describes each color in terms of the quantity of each pigment (cyan, magenta, yellow, and "key" or black) it contains for color printing.

Description
For the mixing of pigments in CMYK color printing, secondary colors are used as they combine ly instead of ly, as they would in RGB. The secondary colors are cyan, magenta and yellow, which correspond to the primary colors of blue, red and yellow. Although shades of gray can be obtained by mixing these three colors in equal proportions, black is included as its own ink in four-color printing for improved color reproduction. This provides the CMYK model. The K stands for "Key" or "blacK", to avoid confusion with the B (blue) in RGB.