It is a service of deliverance from influences of evil spirits, Jesus Christ did it and commissioned His disciples to do so using words “Heal the sick, raise the dead, cleanse lepers, drive out demons” (Mt 10,8). Exorcism (from Greek “exorkizein” means “to curse”) is the command to leave a human being, an animal, place or item, given to the demon in Name of God. It is a special sort of blessing (sacramental) that a priest conducts in certain situations and needs.
The way of expelling evil spirits was taught to the apostles by Christ. Jesus’ exorcisms, just as those conducted by the apostles among the Jews and pagans later on, were famous for their effectiveness. The power over evil spirits is in a way a confirmation of the reality of Christian faith and the fruit of spreading the Good News.