A demon is a paranormal, often malevolent being prevalent in religion, occultism, literature, and folklore. The original Greek word daimon does not carry the negative connotation initially understood by implementation of the Koine δαιμόνιον (daimonion), and later ascribed to any cognate words sharing the root.
In Ancient Near Eastern religions as well as in the Abrahamic traditions, including ancient and medieval Christian demonology, a demon is considered an unclean spirit, more specifically an evil angel, which may cause demonic possession, calling for an exorcism. In Western occultism and Renaissance magic, which grew out of an amalgamation of Greco-Roman magic, Jewish demonology, and Christian tradition, a demon is a spiritual entity that may be conjured and controlled.
Alice Pike Barney - Kate Deering Ridgely (1900)