From DipWiki

Single Elimination

A Single Elimination tournament, also called a knockout, cup or sudden death tournament, is a type of tournament where the loser of each match is immediately eliminated from winning the championship or first prize in the event.

Double Elimination

A Double Elimination tournament is a competition in which a participant ceases to be eligible to win the championship upon having lost two games or matches. It stands in contrast to a Single Elimination tournament, in which only one defeat results in elimination.

See also: Pairing Systems