The difference between spot colors and process colors is simple.

Spot colors are mixed to a specification like paint, you can still specify Pantone colors for print, but when they are printed as spot color, PANTONE 151 C is a bright orange ink that is printed as it mixed.

Process colors are not solid colors at all, but an optical illusion that is mixed in the eye when you are looking at them. If you look at a colored panel in a magazine under a magnifying glass you will see that the color is made up of a pattern of varying sized dots:- cyan, magenta, yellow and black (CMYK).

In this case, PANTONE 151 C is made up of 0% Cyan 62% Magenta 75% Yellow and 0% Black dots and isn’t quite as bright as the spot color version.