A bracket or tournament bracket is a tree diagram that represents the series of games played during a knockout tournament. Different knockout tournament formats have different brackets; the simplest and most common is that of the single-elimination tournament. The name "bracket" is American English, derived from the resemblance of the links in the tree diagram to the bracket punctuation symbol ] or [ (called a "square bracket" in British English). The closest British term is draw, although this implies an element of chance, whereas some brackets are determined entirely by seeding.
In some tournaments, the full bracket is determined before the first match. In such cases, fans may enjoy trying to predict the winners of the initial round and of the consequent later matchups. This is called "bracketology", particularly in relation to the NCAA Men's Division I Basketball Championship. This prediction is not possible in tournaments, such as the FA Cup and the UEFA Champions League, in which the pairings for a later round are not made until after the previous round has been played.
Brackets are commonly found in major North American professional sports leagues and in U.S. college sports. Often, at the end of the regular season, the league holds a post-season tournament (most commonly called a playoff) to determine which team is the best out of all of the other teams in the league. This is done because often in American professional sports there are at least two different conferences, and teams mostly play other teams in their own conference. Examples of this are the American Football Conference and the National Football Conference in the NFL, the American League and the National League in Major League Baseball, and the Eastern Conference and the Western Conference in the NBA or NHL.