Exorcism
In Christianity, exorcism is the practice of casting out demons. In Christian practice the person performing the exorcism, known as an exorcist, is often a member of the Christian Church, or an individual thought to be graced with special powers or skills. The exorcist may use prayers and religious material, such as set formulas, gestures, symbols, icons, amulets, etc. The exorcist often invokes God, Jesus and/or several different angels and archangels to intervene with the exorcism. Protestant Christian exorcists most commonly believe the authority given to them by the Father, Son, and Holy Spirit (the Trinity) is the source of their ability to cast out demons.
Unclean spirit
Such exorcisms are performed rarely by the 21st-century Western church; the more common exorcism involves the ritual preparation of holy water ("aquae"). The 9th-century Stowe Missal preserves an early Celtic formula as "procul ergo hinc, iubente te, domine, omnis spiritus immundus abscedat" ("Therefore at your bidding, Lord, let every unclean spirit depart far from here"). In a Latin version of "The Blessing of the Waters on the Eve of Epiphany" performed in Rome and recorded at the turn of the 19th–20th centuries, the unclean spirit is commanded "per Deum vivum" ("by the Living God"). The modern Latin rite to exorcize holy water banishes any "pestilent spirit" ("spiritus pestilens") or "corrupting atmosphere" ("corrumpens aura"); see Rituals and uses of holy water.