The term is called "Deuce."
You win that game !
Duece is 40-40, and then if you play an add game, it turns into add-out or add-in:)
For the points 40-40 each, the term used in Tennis is 'deuce'.
The scoring in tennis consists of a sequence of points including 0, 15, 30, 40 and game. When both players are tied, say 15-15, it's called 15 all. However, when it's tied 40-40 it's called deuce rather than 40 all.
"40 all" is a shorter term for saying the score of 40-40, or deuce, in a single game (not the match, just the individual game in a set).
In tennis, when both opponents are tied at 40-40, the score is called deuce. Deuce changes to advantage when one opponent scores after achieving deuce.