CMY Coding (Cyan, Magenta, Yellow) is to subtractive synthesis, what RGB coding is to additive synthesis. This model consists in breaking up a color into values of Cyan, Magenta and Yellow.
The absence of these three components yields white while their sum yields black. However, since the black obtained by the sum of the three colors Cyan, Magenta and Yellow is only partially black in practice (and is expensive), printers add a black ink component called pure black. This is known as the quadrichromy, or CMYK model (Cyan, Magenta, Yellow, BlacK).