In tennis, the term for a score of 40-40 is called deuce. When both players reach this score, it signifies a tie, requiring one player to win two consecutive points to secure the game. The first point won after deuce is referred to as "advantage," and if the player holding advantage wins the next point, they win the game. If the player loses it, the score returns to deuce. This scoring system adds tension and excitement, making crucial moments in a match more thrilling.