What does CMYK mean ?
CMYK means Cyan, Magenta, Yellow and Black, where Cyan, Magenta, Yellow are the primary colors in subtractive synthesis. From a theoretical point of view, every possible shade from black to white could be reproduced by combining the CMY colors. In the reality, the lack of purity of the inks used for printing process (e.g ink jet or offset) make it impossible to reach this theoretical black. When adding the maximum quantity of CMY, only a dark brown color can be printed on paper. Therefore, a 'K' or black ink was added in order to get the deepest and purest possible black. A CMYK file consists in 4 composite layers (each will be coded from 0 to 100).