<P> A tennis tournament is organized into matches between players (for singles tournaments) or teams of two players (for doubles tournaments). Very often the tournament takes the form of a knockout tournament consisting of several rounds . In round 1, all players (or teams) are paired (assuming there are no byes) and play a match against each other . The losers are eliminated, and take no further part in the tournament (this is single elimination). The winners are again paired to matches in the next round . The tournament continues until the quarterfinal round (having eight players or teams playing a total of four matches), then the semifinal round (four players or teams, two matches), and finally the final round (with just two players or teams) is played . The winner of the final round is declared the winner of the entire tournament . </P> <P> A tennis match is composed of points, games, and sets . A set consists of a number of games (a minimum of six), which in turn each consist of points . </P> <P> A set is won by the first side to win 6 games, with a margin of at least 2 games over the other side (e.g. 6--3 or 7--5). There is usually a tie - break if the set is tied at six games per player . </P> <P> A match is won when a player or a doubles team wins the majority of prescribed sets . Matches employ either a best - of - three or best - of - five set format . The best - of - five set format is typically only played in the men's singles or doubles matches at Majors and Davis Cup matches . </P>

When is a tie break used in tennis