In tennis, a game score tied at 40-40 is called deuce.
Tennis uses unusual spoken scores: zero is “love,” followed by 15, 30 and 40. When both players reach three points, the score is not normally announced as “40-all”; it is called deuce. The term comes through French, from the expression meaning “two,” referring to the two consecutive points needed to win from that position.
After deuce, the next point gives one player advantage, often announced as “advantage in” for the server or “advantage out” for the receiver. If that player wins the following point, the game ends. If the other player wins it, the score returns to deuce.
The same pattern can repeat indefinitely, so a game may last far beyond the usual four points. “Advantage” is therefore not another name for 40-40; it describes the temporary one-point lead after deuce. In some French-language scoring contexts, the first 40-all score may be announced differently, but “deuce” is the standard English term.