In tennis, an ace is a legal serve that is not touched by the receiver, winning the point for the server. In professional tennis, aces are generally seen on a player's first serve, where the server can strike the ball with maximum force and take more chances with ball placement, such as the far corners of the service box. According to the International Tennis Hall of Fame, this term was coined by the sports journalist Allison Danzig.

A serve in tennis is a shot to start a point. A player will hit the ball with a racquet so it will fall into the diagonally opposite service box without being stopped by the net. Normally players begin a serve by tossing the ball into the air and hitting it. The ball can only touch the net on a return and will be considered good if it falls on the opposite side. If the ball contacts the net on the serve but then proceeds to the proper service box, it is called a let; this is not a legal serve in the major tours although it is also not a fault. Players normally serve overhead; however serving underhand is allowed. The serve is the only shot a player can take their time to set up instead of having to react to an opponent's shot; however, as of 2012, there is a 25-second limit to be allowed between points.