A magical ingredient often used in potions by witches and can also be put in blood for Vampires to drink, which makes the blood nice and spicy. Burba Weed has been mentioned by Spike in Buffy the Vampire Slayer. He has also been seen adding the Burba Weed in his glass of blood.
Buffy: What are you doing, lurking down here?
Spike: I came through the tunnels. Runnin low on Burba Weed. (Holds up some Burba Weed.)
(Buffy looks at Spike confused)
Spike: Stir it in with the blood, makes it all hot and Spicy.