Good question. These terms are thrown around a lot in the printing and graphics world, and it is important to understand the difference.

Check out our video tutorial or continue reading below:

• CMYK (Cyan, Magenta, Yellow and 'Key', or black) are the ink colours used during the printing process. The term 'key' is used instead of 'black' because, really, this is a mixture of the cyan, magenta and yellow inks; the resulting 'black' can be minutely different from one printing company to another.
• RGB (Red, Green and Blue) are the colours of light used by your monitor to display your document on-screen. Black is not listed because on-screen black is an absence of light. A mixture of red, green and blue light produces white.

How does this affect me?
Any image you create on your computer should be created in CMYK mode. This will ensure that the colours you see on-screen will most closely match the final printed product. If you create your document in RGB, the colours in your printed product may vary slightly: many of the bright values produced by your monitor cannot be exactly reproduced in print.

A lot of digital images are JPEG files, and JPEGs are almost always in RGB.