service line

noun

1. Tennis. the rear boundary of a service court.
2. a line running parallel to the front wall in certain court games, as handball or squash, that marks a boundary of the service area.

noun (in certain racket games)

1. the line at the back of the court behind which the server must stand when serving
2. a line indicating the boundary of a permissible service, as on the backwall of a squash court