When to Use It
The only time players will reach a score of duce during a game is when they achieve a tie score at 40-all.
The first time deuce is reached in a game is when each player has won three points, which ties the score at 40-all. However, we don’t say 40-all; instead, we say deuce.
Once the score is deuce, one player needs to win by two. If the server wins the point at deuce, the score becomes ad-in or the server’s advantage. If the server then loses the next point, the score returns to deuce.
If the person returning wins the point, the score becomes ad-out or the returner’s advantage. If the returner loses the next point, the score returns to deuce once again.
This back and forth repeats indefinitely until one player wins two consecutive points in a row.