Pantone colors refer to the Pantone Matching System (PMS), a color matching system used by the printing industry whereby printing colors are identified by a unique name or number (as opposed to just a visual reference). This helps make sure that colors turn out the same from system to system, and print run to print run.  4-color process printing is an imitation of solid colors, which gives the visual impression of the solid colors. They are close to solid colors, but are not exact and vary slightly from print run to print run.