'The Ball is in your court"' means that it's someone else's turn to make a move.
Example of use: "It's not Daniel's fault the deal isn't finished, he made the last offer. The ball is in Harry's court now."
While it is obvious the idiom "the ball is in your court" comes from the world of sports, Scholars differ on whether it comes from the Tennis field or from Basketball. Whichever sports field it comes from, it is a relatively new idiom and was probably used for the first time in the 20th century.