To break serve is to win when your opponent is serving. This is a big deal in professional tennis, when players often dominate when they are serving and matches can turn on a single break. The term up a break means that the player has broken one more time than her opponent during the set. A related term, on serve, means that both players have won all of their service games during a set. A famous example of players struggling to break their opponents was the 5th set of the 2009 Wimbledon final, when it took Roger Federer until the 30th game of the set to finally break Andy Roddick and win the set 16-14 (there is no tiebreaker in the 5th set at Wimbledon). Related terms include break point,break chance, hold serve and back on serve.