Wiktionary
buffyverse
n. (context fandom English) The fictional world, or universe, which serves as the setting for the television series ''http://en.wikipedia.org/wiki/Buffy%20the%20Vampire%20Slayer''.
Wikipedia
Buffyverse
The Buffyverse or Slayerverse is the shared fictional universe in which the TV series Buffy the Vampire Slayer and Angel are set. This term, originally coined by fans of the TV series, has since been used in the titles of published works, and adopted by Joss Whedon, the creator of the fictional universe. The Buffyverse is a place in which supernatural phenomena exist, and supernatural evil can be challenged by people willing to fight against such forces.