A slayer is a young female bestowed with mystical powers that originate from the essence of a pure-demon, which gives her superhuman senses, strength, agility, resilience and speed in the fight against forces of darkness. She occasionally receives prophetic dreams in the few hours that she sleeps.
The opening narration in the Buffy series states "Into every generation a slayer is born: one girl in all the world, a chosen one. She alone will wield the strength and skill to fight the vampires, demons, and the forces of darkness; to stop the spread of their evil and the swell of their number. She is the Slayer."