If you're new to tennis, you probably have some questions about the scoring. For example, you might see a player's score change to "ad," which is short for advantage.
This term is used only when a game is tied 40-all — meaning, each player has scored three times, otherwise known as deuce — and a player must then score two consecutive points in order to win. A player gains the advantage when they've scored once, because they only need one more point to win, while their opponent would need to score twice.
Outside of professional tennis, the term "ad" is also used in a few variations, depending on whether or not the player with the advantage is also the server at the time. Let's say you're serving when you get the advantage — you could say, "ad in" or "my ad." If the opposite happens, and your opponent gets the advantage on your serve, this would be called "ad out" or "your ad."
Either way, if the player without the advantage scores next, the score returns to 40-40, and play continues until someone scores twice in a row. As you can imagine, this can take a long time, especially at the elite level.