They discribe the the base sets of cards ussually just numbers on them unless they are a special kind like gold, silver, they can be sparkle type or insert which are rarer cards which can have letters and number to tell what insert set thier from. You can buy a book called a beckett which tells the prices of tthe cards you have, also numbers tells if the card is extremely rare like1 of 1 which means it is the only one or 20th card out 500 it would look like this on back 20/500 i hope this helps you, its great collecting, i love it.