What is a let in tennis?

A let serve doesn't count as a fault, so the server keeps whichever serve they were on: a let on a second serve is still a second serve. There's no limit on how many lets can happen in a row.

A let is also called when play is interrupted, for example when a ball rolls onto the court during a point, and the whole point is replayed. Some formats play no-let, where a serve that clips the net and lands in stays in play.