A condtion in which a person, place, or object is inhabited and influence
d, or even control
led by, an evil spirit
Ancient civilizations, such as the Egyptians and the Babylonians, believed that disease was caused by possessing spirits and used magical means to drive them out and heal the victim.
The New Testament is full of stories of demonic posession; casting out demons was one of the principal activities of Jesus and his followers. There is likewise evidence of a Jewish belief in the phenomenon and a tradition of magical exorcism via the use of angelic names, though the driving out of evil spirits by anyone other than angels is not mentioned in canonical Jewish literature.
There have been many tragedies enacted throughout history in which a case of mental illness (or even simply holding an unpopular set of ideas) has been attributed to possession. Since the 1500s the Church has been increasingly cautious about its diagnoses in such matters, preferring to assume that a phenomenon is natural unless no other explanation but the supernatural can be found.