Spot colors are colors which are printed with their own premixed inks. You can choose from several spot color systems and from hundreds of different spot-color inks. In spot-color offset printing, each spot color is reproduced using a single printing plate. In contrast, process color printing uses four inks only (CMYK: cyan, magenta, yellow and black) to reproduce all colors.
If you print a spot color at 100%, a solid opaque color appears on your page (not a dot pattern). A tint of a spot color, i.e. a lightened spot color, is created by printing smaller halftone dots of the base color.
Spot colors can provide excellent results when used for offset printing. For digital output or monitor display, however, spot colors are less well-suited and should be used with caution.