The term otherkin originally only implied individuals who believed themselves to be fairies, elves, or changelings. In time the term has been broadened to include other supernatural creatures such as witches, vampires, werewolves, unicorns, dragons, mermaids, angels, demons, and even aliens. Additionally, people who believe themselves to be reincarnated animals are also included under the umbrella of otherkin.
One should show extreme caution when attempting to label someone as being otherkin, as many people object to such classification. For example, most people who believe themselves to be witches, vampires, or werewolves take much offense to the label. Those people who consider themselves fairies or elves tend to be the most accepting of the label.
Otherkin FAQ
Reference: new-generation-witch.blogspot.com