'Thick Cloud' in the Bible

And [so] you came near, and you stood under the mountain, and the mountain [was] burning with fire up to the heart of the heaven, {dark with a very thick cloud}.

"These words Yahweh spoke to your whole assembly at the mountain from the midst of the fire and the very thick cloud [with] a loud voice, and {he did not add anything}, and [then] he wrote them on two tablets of stone and gave them to me.