Dampener: A small rubber device affixed to the strings of the racket to absorb some of the vibration caused by hitting the ball.
Dead net (or dead net cord): Situation in which a player scores by inadvertently hitting the ball in such a way that it touches the upper cord of the net and rolls over to the other side. An example of this would be Tightrope Walking.
Deciding point: In doubles, the point played when the game score reaches deuce and there is no ad play; the game is decided in favor of whichever team wins the deuce point.
Deep shot: Shot that lands near the baseline, as opposed to near the net or mid-court.
Default: Disqualification of a player in a match by the chair umpire after the player has received four code violation warnings, generally for his/her conduct on court. A double default occurs when both players are disqualified.
Deuce: Score of 40–40 in a game. A player must win two consecutive points from a deuce to win the game, unless the tournament employs deciding points. A player who has won one point after deuce is said to have the advantage.
Deuce court: Right side of the court of each player, so called because into which the ball is served when the score is deuce.
Dink: Onomatopoetic term for a shot with little pace, usually hit close to the net.
Disadvantage: Player or team which is 40-advantage down.
Double bagel: Two sets won to love.
Double fault: Two serving faults in a row in one point, causing the player serving to lose the point.
Doubles: Match played by four players, two per side of the court. A doubles court is 9 ft (2.97m) wider than a singles court.
Down the line: Ball hit straight along the sideline to the opponent's side of the court.
Draw: The schedule of matches in a tennis tournament. The starting fixtures are determined by a combined process of player seeding and random selection, and may or may not involve a public draw ceremony.
Drive Volley (or swing volley): Attacking type of backhand or forehand volley usually executed from a position in mid-court and played with pace at shoulder height.
Drop Shot: Play in which the player hits the ball lightly enough to just go over the net, usually with backspin; designed to catch a player who is away from the net off guard.
Drop Volley: Drop shot executed from a volley position.