Elteri

The word "Elteri" means something close to "outsider" or "alien" and is used to describe intelligent creatures who are not natives of the mortal plane of existence. Some Elteri are summoned to our own dimension through powerful magic; others end up here through happenstance or through their own free will. Though some are bound or trapped in our reality and a few stay here by choice, most can and often do come and go as they please. 
Elteri tend to be very long-lived (if not immortal) beings and some wield magical powers that rival the gods themselves. This power can be used to the benefit of humans who make pacts with the Elteri, but this can be a dangerous endeavor. Elteri often operate on a scale that is incomprehensible to humans, orchestrating plans that can last centuries and stretch across multiple realities. This makes it nearly impossible for mortals to know where they stand with an Elteri, which can be their downfall. While Elteri usually only deal with mortals when approached, they do take interest in, quietly assist, or grant favors to humans whose activities or destinies serve the Elteri's purposes. 
In addition to the blanket term "Elteri," certain kinds of outsiders are known by other names with varying degrees of specificity. 

• Demon is a generic term for malicious and usually monstrous Elteri.
• Szeraf is a general term for benevolent Elteri. 
• Irshe are a type of Elteri whose dimension is so close to our own that they can often be sensed even when not seen and events in their reality can affect those in our own (and vice versa). Except for their long lifespans and magical powers, Irshe are very similar to humans; They farm, raise children, go to war, and do many of the other things humans do, and their culture and society is a weird mirror of our own. Irshe are masters of twisting words to their own ends, so one must be extremely precise when making a pact with these creatures. 
• Ilye are Elteri who command a particular element. In addition to the four central elements (fire, air, water, and earth), there also lesser Ilye who represent specific forms of the elements or other natural phenomena. There are Ilye with dominion over ice, lightning, and dust, for example. 
• Vashi are animal gods. Some appear on our plane as perfect specimens of the animals they rule, but most take the form of human-animal hybrids or humans with animal-like features. Like humans, animals have different gods for different aspects of life, so a cat vashi is equally likely to be the god of stealth, the hunt, or playing with balls of yarn. 
• Incubi and Succubi are Elteri who feed on the life force of humans during sex. 
• Familiars are lesser Elteri who wizards can bind in animal form to serve as servants.