What is the "squelch" for on police scanners?

Answer 1

It lets the device stay silent when there is no action.
The sound only comes on when a voice signal comes on,
You generally turn on the squelch just at its working minimum ( hope that makes sense). You do not turn it all the way to the max.
You would block all incoming sounds and hear nothing at all if the police were using their radios

Answer 2

It filter out noise.
I may not be correct.
I not sure if this any better to understand, it wiki;
http://en.wikipedia.org/wiki/Squelch

Answer 3

it's the emergency call for "more donuts"