Pantone naming convention is a numbers followed by various different letters. The letter suffixes denotes how that particular color will appear on uncoated, coated, or matte finish papers. The coating and finish of the paper affects the apparent color of the printed ink even though each uses the same formula.

When selecting a PMS color you want to make sure you are looking at the appropriate swatch book in regards to the stock you will be printing your project on. If you are printing on an uncoated stock such as Cougar you want to look at the uncoated (U) swatches. If printing on a glossy coated stock such as McCoy Gloss you want to look at the coated (C) swatch book.

U = uncoated paper
C = coated paper
M = matte paper
CV = computer video (electronic simulation)
CVU = computer video - uncoated
CVC = computer video - coated