system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the abbreviation of 'Cyan, Magenta, Yellow and Black' called 'CMYK' and not 'CMYB'?
gpt
So the CMYK is referring to the plates of Cyan, Yellow, Magenta, and Key. 

This key plate is usually the last plate, and is what provided the details via lines and contrast in black ink. You can look at a print and see how there's usually not much in actual detail until the black key is used. As such it's also the key for aligning the plates, as the others need to be aligned in relation to it, since if its off at all, the whole image will look wrong when the lines and contrast are laid down.