Why is black referred to as 'K' in CMYK?

In the CMYK color model, black is referred to as 'K' because it is considered the key color in the printing process. Black ink is used to create depth and detail in printed images, which is essential for achieving high-quality output. The term "key" indicates that this color is crucial for defining the overall clarity and definition of the printed materials.

In practice, black ink serves to enhance contrast, particularly in graphic design and photography, making the colors printed using cyan, magenta, and yellow more vibrant and distinct. This is particularly important because the other three inks do not produce a satisfactory black on their own and can result in color muddiness if mixed. Therefore, using black as the key color optimizes the printing process by providing a solid foundation for the image.