Let
Do you mean "let"? If so, a let is when a serve touches/nicks the net AND lands in on a player's serve. People call "let" so the server knows their serve hit the net. If a server hits a let, they get to redo their serve.
When the first serve is a let.
a serve
Fault
Fault
It would called as 'let' and server gets another chance to serve.
In professional tennis, there are line judges for that. In non-professional tennis, however, a server can call his or her own serve out. Most do not because it is a point against them, even though the opponent thought the serve was in.
Because a serve hits the net.
Let is from the word filet, a French word for the net. In tennis, it is a type of serve that is not valid and has to be done again.
Because you hit the ball with some kind of racket and that is why you call it a serve.
It is called a 'Let'