'Mystery' in the Bible

The king answered Daniel and said, “Most certainly your God is the God of gods and the Lord of kings and a revealer of mysteries, since you have been able to reveal this mystery!”

‘O Belteshazzar, chief of the magicians, because I know that a spirit of the holy gods is in you and no mystery baffles or troubles you, tell me the visions of my dream which I have seen, along with its interpretation.