Smiting

Smiting is an angelic ability that can kill demons, monsters and humans. Although this power inherently allows angels to easily dispose of demons, it has its limitations. Smiting will not work if the angel is physically and mentally too weak. Regular angels are able to smite most demons except the most powerful, as displayed when Castiel as a regular angel was unable to smite Alastair, a high ranking demon. An angel also cannot smite a demon not possessing a vessel. If a demon has been smote, the vessel's eyes light up with a white holy light, burning the eyes and killing the demon.

Seraphs and Archangels however are many times more powerful than their regular angel brethren and can smite any demon. As a testament to their power, Castiel as a Seraph was able to frighten the King of Hell into retreating when he threatened to smite him.

The ability to smite a demon or a monster is inherent in an angel. According to Dean, it was like riding a bicycle. Once learnt, one would remember it for life. Cupids are the only angelic being that have not shown the ability to smite.

Rit Zien, the medics of Heaven, have a different form of smiting, one so absolute that it completely destroys the entire body. It is nearly completely painless and designed for use on Angels who are mortally wounded, to give them a painless death.

Angels have used this ability to kill humans in the episode Holy Terror.

The demon Cain displayed a similar power except the light was red instead of white and could apparently kill all but the Knights of Hell.