An ace is a serve that a player is not able to reach when it is served to them. This means that an ace is when a player serves it in the correct service box of their opponent but the opponent is unable to even get their racquet on the ball.
An ace is considered a winner as it grants a point to the server. Scoring an ace shows the strength and power of a player as well as their accuracy in serving a ball to a particular spot on the court where their opponent cannot reach it.
As of 2017, famous tennis player Ivo Karlovic holds the record for most aces in a career with a crazy total of 12,278. In 2017 Karlovic took over a match at the Australian Open and set a record with 75 aces in a match.
John Isner holds the official record from the ATP for the fastest ace ever recorded at a speed of 157.2 miles per hour. However, Sam Groth has the fastest unofficial speed for an ace that has ever been recorded with a whopping speed of 163.4 miles per hour.