Possession is the supernatural ability to intrude the bodies of individuals and take control of them. This ability is possessed by Spirits, who can use it to take control of the living and other supernatural beings.
When possessing another, Spirits take full control over the body, though whether they are able to access their minds and memories is dependent on the Spirit and the possessed. Beings with a strong will can resist the intrusion of their minds and may be able to break free of possession entirely. However, in most cases, the spirit must leave out of free will or be forcefully expelled.