'Thick Cloud' in the Bible

And Jehovah said to Moses, Lo, I come to you in a thick cloud, that the people may hear when I speak with you, and believe you forever. And Moses told the words of the people to Jehovah.

And it happened on the third day in the morning, that there were thunders and lightnings, and a thick cloud upon the mountain. And the voice of the trumpet was exceedingly loud, so that all the people in the camp trembled.