Exorcism
In Catholic Christianity, exorcisms are performed in the name of Jesus Christ. A distinction is made between a formal exorcism, which can only be conducted by a priest during a baptism or with the permission of a bishop, and "prayers of deliverance" which can be said by anyone.
The Catholic rite for a formal exorcism, called a "Major Exorcism", is given in Section 11 of the Rituale Romanum. The Ritual lists guidelines for conducting an exorcism, and for determining when a formal exorcism is required. Priests are instructed to carefully determine that the nature of the affliction is not actually a psychological or physical illness before proceeding.
Exorcist
In some religions, an exorcist (from the Greek „εξορκιστής“) is a person who is believed to be able to cast out the devil or other demons. A priest, a nun, a monk, a healer, a shaman or other specially prepared or instructed person can be an exorcist. An exorcist is a person who performs the ridding of demons or other supernatural beings who are alleged to have possessed a person, or (sometimes) a building or even an object.