'Unclean Spirit' in the Bible

Jesus having called his twelve disciples, he gave them power to cast out unclean spirits, and to heal diseases and disorders of every kind.

When an unclean spirit is gone out of a man, he roams about the deserts, seeking rest, and findeth none.

and when the unclean spirit had thrown him into convulsions, with a loud cry, he came out of him.

at which they were all so amazed, that they ask'd one another, what's the meaning of all this? what new doctrine is here? for he commands with authority even the unclean spirits, and they obey him.

and I saw three unclean spirits like frogs come out of the mouth of the dragon, and out of the mouth of the beast, and out of the mouth of the false prophet.