A Demon is the name for the inhabitants of the Nethervoid which can be called forth and bargained with via the magic of demonology. Prior to the end of the Great War demons were apparently able to escape the Nethervoid without aid. Whether summoned or freely able to move about, they were a significant part of the life of the Northern Empire, enough that the Empire fielded a number of half demon warriors known as shatra.
It is known that demons are sometimes able to "listen in" on prayers and respond to summons by practitioners of theurgy, while the gods state flatly that demons and those who frequently associate with them "stink," and may even fail to recognize the individual exists at all. Unlike the gods, demons see all humans as human beings whether they are magicians of any kind or not.
Demons are typically referred to as belonging to a particular Circle, indicating the relative difficulty in summoning them or relative price the demon requests for service. When summoned, demons may require sacrifices in the form of gold, blood, or lives (not necessarily human ones).
Unlike the gods which are constrained, acting only when asked and if proper conditions have been met, demons are restrained- acting freely within the limits imposed upon them and requiring permission to act outside those constraints.
See: Category:Demon for a partial list of Demons