O que significa the ball is in your court?

There's a very famous american daily weekday radio program called Elvis Duran and the morning show and I've been listening to it for some years. Since I'm in Brazil I have to listen to it on demand on one of these audio streaming services like Spotify (in case you're interested). 

It's very common for these radio shows to read daily horoscopes of all zodiac signs. My sign is cancer and I remember my horoscope for yesterday, July 26, started like "the ball is in your court. It's time to take action." Do you know what that means?

My horoscope was encouraging me to take responsibility for further action, especially after someone else previously held it for me. It becomes intuitive to think that in tennis if the ball is in your court it is your turn to hit it. That's all for now. Bye bye