Whenever you pick up a magazine or full color newspaper you are looking at the product of what is called "four color process" printing. It is a worldwide standard for printing color, but what does it really mean?
It is quite an amazing procedure. Basically we can break down all real world color into four primary colors: Cyan (light blue), Magenta (a purplish red), Yellow and Black. This is what is known as CMYK (K is for Black). Back in the old days a camera was set up with different filters and screen angles and four separate photographs were taken of an image to create the CMYK separations. Today, computers handle this complicated process with ease.
If you have a very strong magnifying glass you can actually see how this works. Take any full color picture (it can be a from a magazine, a brochure or even a product label) and have a really close look at it. What looks like smooth color is actually a series of very small dots - and these dots are made up of just four colors - Cyan, Magenta, Yellow and Black. But with high resolution printing, the naked eye will not see any of the dots, it will just look like a smooth full color image.
Four color process printing is just printing a full color image using these four colors: Cyan, Magenta, Yellow and Black.