All these terms refer to demons, which are spirit beings that oppose God's will.
* God created angels to serve him. When the devil rebelled against God, some of the angels also rebelled and were thrown out of heaven. It is believed that demons and evil spirits are these "fallen angels."
* Sometimes these demons are called "unclean spirits." The term "unclean" means "impure" or "evil" or "unholy."
* Because demons serve the devil, they do evil things. Sometimes they live inside people and control them.