[2Jedismom]

Perhaps the void is the "shadow world"?

[Scene goes back to Strider and the Hobbits at the Trollshaws. Frodo is delirious]
Sam: Mr. Frodo? He’s going cold!
Pippin: Is he going to die?
Strider: He’s passing into the shadow world. He will soon become a wraith like them.
[Frodo gasps]
[The Nazgul cry is heard from a distance]
Merry: They’re close.

[Penny1]

I was wondering about that possibility, 2J. That may be what is meant--the shadow world that Frodo only sees when he has the ring on and later when he is wounded by the morgul blade could be the "void" Sauron is talking about.