There are many beings who are not of this plane of existence. These beings, known as Outsiders, tend to be magical in origin. They are a sentient race, likened to Elves or Humans, however they tend to have a higher innate level of power. The most commonly known types of outsiders are Demons, Spirits, and Fae.
Demons and Spirits in particular are known for the fact that they can breed with mortal races, creating a hybrid that has at the very least some innate magic, even if the person in question has no formal magical training. This can be especially witnessed when trying to harm a half-outsider with elemental magic, which they find to be particularly easy to evade, for a limited time.
The half-breed children of Outsiders tend to be referred to as Outsiders by the mortal races, for ease of communication. They tend to be respected or feared, if brought up in a mortal society. How they are treated by their magical kin varies from race to race.
All Outsiders are categorized into two distinctions: Greater (or True) and Lesser. A Greater denotes one who is a full-blooded Outsider. Any Outsider who is not a full-blooded but still is considered an Outsider of that species is noted as a Lesser.