Buffyverse

The Buffyverse is a fictional universe created by writer/director Joss Whedon. It is the setting used for the movie Buffy the Vampire Slayer (BtVS), the BtVS television series and the Angel television series.  Comic books and novels based on both the Buffy and Angel television series and the Fray comic book also take place in the Buffyverse. The term Buffyverse was created by the fans of the shows and later used by Whedon as the name for his world. The term has also been used in the titles of published works.

The Buffyverse is a world where Vampires and demons exist. Many different types of fictional creatures and monsters can be found in this world. These creatures include werewolves, ghosts, trolls, and witches. It is a world where magic is used often. Most of the people in the Buffyverse do not know that these creatures live in this world or that magic exists.

Notable features
The Slayer
The Slayer or Chosen One is a young girl with super-human strength, agility and stamina. It is her destiny to fight evil. When one Slayer is killed, a new girl is chosen to become the new Slayer. The new slayer has all of the power of the last Slayer as soon as she is chosen. The new Slayer also begins to have dreams that tell her of her future and Slayers from the past.

The first Slayer was created long before written history by a group of men who looked like Aborigine. She was created by combine her with a demon. As each Slayer is killed, the demon moves to the next slayer. It gives her the powers of the Slayer as well as the dreams of its past with the other slayers.

 Hellmouth 
In the Buffyverse there are many different dimensions or worlds. Some are full of evil. A place where the borders between the normal world and an evil dimension are weak is called a Hellmouth. Evil in the normal world will naturally move towards a hellmouth. The area closest to a hellmouth will be home to much evil and strange circumstances.

There are two well known hellmouths in the Buffyverse. The first is located in Sunnydale, California. This is the place where the stories in Buffy take place. It is the largest and most powerful hellmouth in the Buffyverse. The second hellmouth is in Cleveland, Ohio. Not much is known about this hellmouth.

References

 Other websites 

Fan forum
Buffyverse dialog database