This tennis bet is based on whether the server "holds serve" (i.e. wins the game while serving) and how many points his opponent scores in the game; or if the server is "broken on the serve" (i.e. loses the game while serving).
An easy way to describe this would be to imagine a "Score of game 3 of set 1 or break" match between Player A and B, where player A serves.
Player A to 15means A will win with a greater score than Player B’s score of 15 points.
- A bet on
Player A to 40means A wins while Player B scores 40 points.
Break betmeans that Player B wins the game served by Player A.