Watching this match from 2006 at 17:23 Lin Dan serves and the judge calls "let" or "net", the serve lands in, and Lin Dan gets to serve again. I can't tell if the serve hit the net, but I didn't think there was a "let" in badminton. I thought if the serve hits the net but lands in or would land in it's playable. https://youtu.be/eAJWcs340iI?t=17m23s
Looks like he served before LCW was ready - you can see that he still has his hand up as the shuttle crosses the net.
First, let's sort out the obvious: There's no call "net", although various calls do include "net": There is a call "let", although nowadays umpires are encouraged to say "Play a let". §14 of the BWF laws explains it in detail: The umpire judges whether a receiver is ready. Players have an understanding that to be considered ready, the receiver puts their racket up, and to signal otherwise the receiver holds their non-racket palm towards the opponent. If you look closely, you'll see that the latter is what's happening here: Apart from the receiver not being ready, other common causes for a let are a shuttle from another court falling onto the current one, and unsighted umpires when playing without line judges.
