What (who) is CMYK - definition

SUBTRACTIVE COLOR MODEL, USED IN COLOR PRINTING

Four-color printing; CMYK color space; CMYK; Process color; CYMK; CMYK colour model; Cmyk; Cyan, Magenta, Yellow, and Key Color Model; Cmyk color; CMYK color separations; CMY color model; CMYB; CMY color space; CMY color; CMYK color; Cmy color model

CMYK

Cyan Magenta Yellow blacK (Reference: color system, DTP)

CMYK

<graphics> cyan, magenta, yellow, key. A colour model that describes each colour in terms of the quantity of each secondary colour (cyan, magenta, yellow), and "key" (black) it contains. The CMYK system is used for printing. For mixing of pigments, it is better to use the secondary colours, since they mix subtractively instead of additively. The secondary colours of light are cyan, magenta and yellow, which correspond to the primary colours of pigment (blue, red and yellow). In addition, although black could be obtained by mixing these three in equal proportions, in four-colour printing it always has its own ink. This gives the CMYK model. The K stands for "Key' or 'blacK,' so as not to cause confusion with the B in RGB. Alternative colour models are RGB and HSB. (1994-12-22)

CMYK

Acronym for Cyan, Magenta, Yellow, and Black (don't ask me why K stands for black). Theoretically, when properly and applied to white paper, these colors can replicate any visible color. Actually, some colors need to be pre-mixed.
This appears yellow, so we'll reduce its yellow CMYK component.

Wikipedia

CMYK color model

The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation CMYK refers to the four ink plates used: cyan, magenta, yellow, and key (black).

The CMYK model works by partially or entirely masking colors on a lighter, usually white, background. The ink reduces the light that would otherwise be reflected. Such a model is called subtractive because inks "subtract" the colors red, green and blue from white light. White light minus red leaves cyan, white light minus green leaves magenta, and white light minus blue leaves yellow.

In additive color models, such as RGB, white is the "additive" combination of all primary colored lights, black is the absence of light. In the CMYK model, it is the opposite: white is the natural color of the paper or other background, black results from a full combination of colored inks. To save cost on ink, and to produce deeper black tones, unsaturated and dark colors are produced by using black ink instead of the combination of cyan, magenta, and yellow.

https://en.wikipedia.org/wiki/CMYK color model