Crossbow - weapon that has a bow fixed crosswise on a wooden stock, with grooves on the stock to direct the projectile.
Demon - Evil supernatural being
Feeding - "To make you a vampire they have to suck your blood. And then you have to suck their blood. It's like a whole big sucking thing. Mostly they're just gonna kill you. Why am I still talking to you?"
-Buffy, "Welcome to the Hellmouth"
Ghost - spirit of a dead person
Holy Water - a type of water blessed by a priest and used for religious purposes.
Host - person whom the vampire feeds on.
Sire - A term for a Vampire that turns a human into a Vampire
Slayer - "A girl born once every generation with the strength and skill to hunt vampires, find them where they gather and stop the spread of their evil and the swell of their numbers."
-Narrator
Stake - A piece of wood pointed at one end for driving into a vampire's heart. Used for killing vampires.
Vampires - "The books tell the last demon to leave this reality fed off a human, mixed their blood. He was a human form possessed, infected by the demon's soul. He bit another, and another, and so they walk the Earth, feeding... Killing some, mixing their blood with others to make more of their kind. Waiting for the animals to die out, and the old ones to return."
-Giles explaining the origins of vampires, "The Harvest"
Watcher - a person that finds the Slayer and guides her path.
Werewolf - a living human being transformed into a wolf or capable of assuming the form of a wolf.
Wicca - pagan nature religion.
Witch - A woman believed to have supernatural powers.