Questions about the sport of tennis.

Tennis is a racquet-and-ball sport in which two players or pairs take turns hitting a ball with their racquet, sending it over a net in the center of the court to the opposing player or side.

Modern tennis is played on a court, 78 feet long (marked with two "back lines") and 27 feet wide (36 feet for "doubles" tennis, marked with "side lines"). The surface of the court may be a hard surface (often concrete, common for recreational courts due to the durability and low cost of maintenance), clay dirt, or grass. The court is divided in half by a net 3 feet 6 inches tall at the posts (dipping to 3 feet even in the center). Each half is divided roughly in half again with a line 21 feet from the net called the service line, and a line perpendicular to the service line is drawn between the service lines and is called the center line. Players each have one racquet, used to hit a pressurized but not re-inflatable latex ball with a green fuzzy covering.

A "point" or "rally" begins with a "serve"; an initial hit at the ball made by the serving player behind the player's "back line". One player serves for all points in a game, and then the serve passes to the opposing player for the next game. The player may not cross the back line while serving (a "foot fault"), and the ball, after being struck, must pass cleanly over the net, cross the center line, and bounce in front of the opposite service line and in-bounds (failure to do any of these is a "fault"). After this is done (a player committing a fault gets a second try, and on a "double fault" a point is awarded to the other player), the opposing player must then hit it before it bounces a second time, and again must send it cleanly over the net but it may bounce anywhere between the side lines and before the back line. Players then take turns hitting the ball over the net to each other, until one of three things happens: the ball bounces twice on one side of the net; the ball takes its first bounce "out of bounds" outside the side lines or behind the back line; or the ball fails to cross the net before bouncing after having been struck by a player. When one of these happens, the player who last played the ball successfully (from their racquet across the net and in bounds) wins the rally and is awarded a point.

Players must score four points, and at least two more than their opponent, to win a game. Points in a game have special terms, progressing from "love" (zero) to 15, 30, 40, and then "game". A game tied 40-40 is said to be at "deuce"; the player who wins the next point has the "advantage", and if they win the next point they win the game, otherwise the score returns to "deuce". A "set" is won by the first player to win at least six games and at least two more than their opponent (though in most tournaments, if any set but the final set is tied 6-6, the next game decides the set). A "match" (the normal "deciding unit of play" in competitions and tournaments) is won by the first player to win two out of three sets, or three of five for certain men's tournaments. There is no predefined time limit, and usually there is no tie-breaking game in the last (third or fifth) set of the match, so tennis matches may be quite long; the longest Wimbledon final in history, played in 2008 between tennis greats Roger Federer and Rafael Nadal, lasted for four and a half hours of actual play, with two rain delays adding an additional three hours.

Tennis is played recreationally between casual players on local courts maintained by municipalities or local gyms, and competitively at the middle school, high school, college and professional levels. Four historic "Grand Slam" tournaments are held each year, in Melbourne, Australia (the Australian Open), Paris, France (the French Open), London, England (Wimbledon) and Queens, New York (US Open), with the winner of each receiving prize money in the millions of US dollars.