What at Wimbledon what does the display challenges remaining mean?

Answer 1

A new system is being used that monitors the court lines. The old system (called Cyclops) has been replaced with a new system called Hawk-Eye. The new system stays quiet and is only used if a player disagrees with a line judge's call.

When a player challenges call and is found to be wrong they loose one of their remaining challenges. You get new challenges every set and an extra challange during a tie-break (assuming Wimbledon are using similar rules used on the Australian and French opens).

The new scoreboards are video walls, so hopefully we'll also see some video playback of contencious calls...!! :)

Answer 2

They are the hawkeye challenges players have left... i.e. if Nadal has 3 challenges left he can question the linesmen/umpires about calls made and they will use hawkeye. If he is right he doesn't lose that challenge and he will have the same amount of challenges. In tie-breakers players get one extra challenges