'Unholy' in the Bible

You shall not offer any strange incense on this altar, or burnt offering or meal offering; you shall not pour out a drink offering on it.

Now Nadab and Abihu, the sons of Aaron, took their respective [ceremonial] censers, put fire in them, placed incense on it and offered strange (unauthorized, unacceptable) fire before the Lord, [an act] which He had not commanded them to do.

and to make a distinction and recognize a difference between the holy (sacred) and the common (profane), and between the [ceremonially] unclean and the clean;

But Nadab and Abihu died [in the presence of God] when they offered [in their ceremonial censers] strange [unholy, unacceptable, unauthorized] fire before the Lord.

“When you come to appear before Me,Who requires this of you, this trampling of My [temple] courts [by your sinful feet]?