All except the grumpiest, scariest medieval 'ghosts' who were called 'revenants' and were the animated corpses of the returning dead. The notion of a witch as a woman who flies through the night, with the big hat, green face and evil agenda is relatively recent folklore. They used turnips instead of pumpkins. Children suspend the carved root from string or a forked stick and carry it around when they go out at night. Set against a backdrop of contemporary cynicism and ancient exorcism, it uses the conventions of the horror film to examine issues of belief, trust, faith and love.
Exorcism is the rite of driving out demons.
During the Golden Age of Reformation the Catholic Church used exorcism to demonstrate its superiority over the newer protestant religions. We get pushed around, and believe we can't be instrumental in our own environment. The possessed or evil characters are able to regain that control, because they can say or do things they otherwise couldn't. You can only be possessed if you are not in a state of grace. Sinners can be possessed but not children.