It is a fairly empty zone of space. Fairly empty. There is a cloud of slighty energized particles there. Not dense enough to be a visual obstacle, or even a real navigational one, but enough to be measured. And to have a real effect. Most people go around it, just to be safe. Others, just run right through all the time.
If you listen to it on the wave channels, it is a strong hydrogen wave… a strong solid tone. (The Quiet really isn’t that quiet).
The partical field is charged enough to absorb and eliminate communication and most broadcasts. It puts a dent into sensor reception. You can navigate through the use of a keen eye or a visual capture and some computing, as the beacons can’t be heard in The Quiet. If something happens to your computer and you don’t have a good navigator (with an old sextant and star chart) you could be in quite a bit of trouble.
And things can happen. In the Quiet there are areas of "high concentration". Those areas could discharge to a passing ship knocking out some of the system. The computer is the most likely canidate, but lighting and comm are also possible. Actually anything could break given enough discharge. Including your ships field dampers. Thus the discharges could get worse.
And in the worst possible world, the strong signal could effect the minds of those with leaky or slightly leaky brain pans. Unless they are wearing their tinfoil caps, they will go a bit more odd.
(The good thing is that all reavers in the quiet go even more nutz and start eating each other).
Remember, in The Quiet nobody can hear you scream.