exist in a wide variety. In general, they are horrifying creatures from other planes of existence. They range from some of the denizens of Hell to "ordinary" dimensional travelers.
The drum, bass, guitar, music, noise archetypes existing in the Vurt.
In the Shannara series by Terry Brooks, there are several creatures known as Demons. They call themselves Jarka Ruus, which means 'banished peoples'. These creatures were long ago sealed within the Forbidding, a realm of darkness where only the cursed dwell.