Spot colors are premixed or special mixed inks that make a Pantone color or standard color. (A standard color is one that is premixed at the factory so its the color you want right out of the can. Special Mixed or Pantone colors are like going to a paint store and looking at paint chips. Then after choosing the color you want the paint person "mixes" that color for you). Spot colors can achieve colors that are out of gamut or "range" of 4 color process colors. Spot colors, depending on the ink color and how many colors, is usually a cheaper form of printing than 4 color process but you are limited to that color and any tint variant of that color. (Example: You pick a Red Spot color we can print any tint percent or "shade of that Red but we could not make it a blue without using another color ink.) The easiest example to understand is think of Spot colors as going to a hardware store and buying paint. You want to paint a wall blue you get blue paint. If you want shades or tints of that blue you mix in white. But that is the only color variance you can achieve without purchasing more colors of paint.