'Obscurity' in the Bible

And ye came near and stood under the mountain; and the mountain burned with fire to the heart of heaven, with darkness, clouds, and obscurity.

These words Jehovah spoke to all your congregation on the mountain from the midst of the fire, of the cloud, and of the obscurity, with a great voice, and he added no more; and he wrote them on two tables of stone, and gave them to me.