K in CMYK stands for Key , or Key plate —the black plate used to add detail and help align the other colors in printing. In everyday use, people often just say it means black, because the K channel in CMYK represents black ink.

Quick Scoop

  • CMYK = Cyan, Magenta, Yellow, Key.
  • K = Key, not the letter “B” for black.
  • It’s called Key because it’s the main plate that other printing plates line up with.

TL;DR: K stands for Key , and in practice it refers to black in print workflows.