When a serve touches the net cord and lands in the correct service box, it is called a let. The serve does not count as a fault, but the point is stopped and the server normally repeats that service attempt.
A let can happen because the ball’s path changes slightly after brushing the net. Under standard professional tennis rules, the receiver must wait for the serve to be replayed. If the ball touches the net and fails to land in the correct service box, however, it is a service fault rather than a let.
The distinction between a let and a fault is a common source of confusion. A fault also occurs when the serve lands outside the service box, fails to clear the net, or violates serving-position rules. A second fault on the same point is a double fault, which awards the point to the receiver.
The word “let” is also used more broadly when play is interrupted and a point must be replayed. In professional tennis, the chair umpire usually announces “let” or “net” to signal the replay.