Net cord

The white canvas band along the top of the net, which a low shot sometimes ticks and then sails over. During the play of a point, this is usually of no significance and play continues, but sometimes contact with a net cord produces so erratic a result that the ball is unreturnable. If a ball hits the net cord on a serve, and the serve lands in the proper box, a let is called and that attempted serve simply doesn't count at all and is retaken.