What is the difference between RGB and CMYK?

Simply put: the difference between these two ‘color modes’ is that RGB represents what can be displayed on Screens, and CMYK is limited to what can be reproduced in Print.
RGB [Red, Green, Blue] = 16M colors
CMYK [Cyan, Magenta, Yellow, Key*] = 160k colors
*In traditional printing, the plates are aligned with the Key plate [black]