Also a tennis term for when the server commits two "illegal" serves (faults) consecutively. Illegal serves could be due to foot faults, or failure to hit the ball into the required portion of the receiver's court (diagonal from the server and in the part of the receiver's court closest to the net).

The receiver (or receiving team in doubles) earn a point when the server double faults.

Double faults are not cumulative. In other words, if the server double faults and then commits a 3rd consecutive fault, this 3rd fault would be considered the same as a 1st fault.