All cards are identified by rarity. There are five "core" rarities: common, uncommon, rare, very rare, and extremely rare. There are also special rarities: chase and variant. (Variants are given to variations of other cards and have since been retired for new series.) Chases are special in some way.
Each series detail page will show the number of copies of each rarity, along with the odds of receiving a card of any given rarity.