'Expanse' in the Bible

Now over the heads of the living beings there was something like an expanse, like the awesome gleam of crystal, spread out over their heads.

Under the expanse their wings were stretched out straight, one toward the other; each one also had two wings covering its body on the one side and on the other.

And there came a voice from above the expanse that was over their heads; whenever they stood still, they dropped their wings.

Now above the expanse that was over their heads there was something resembling a throne, like lapis lazuli in appearance; and on that which resembled a throne, high up, was a figure with the appearance of a man.

Then I looked, and behold, in the expanse that was over the heads of the cherubim something like a sapphire stone, in appearance resembling a throne, appeared above them.