Otherkin/Therianthrope: People who involuntarily identify on a non-physical level as a non-human being. This can occur for spiritual or psychological reasons (which are not to be confused with mental illness). When speaking of the identity in general, the following terms are used: Therianthropy and otherkinity (or simply "otherkin").
Fictionkin: People who involuntarily identify as fictional species/characters. Very much similar to otherkinity but with people and/or beings that haven't quite made it to legendary/mythical status. This is known as "fictionkinity".
System: Two or more people/creatures in one body. Can be caused by trauma but can also occur without it.
Animal/Other-hearted: Also known as "kith", these are people who feel a deep connection and empathy with a certain creature that is so deep, they almost identify as said creature(s) but not quite.
Coping/Otherlinker: A person who uses fictional characters and non-human beings as a way to cope with some problem. Voluntarily identifying as something non-human.
Subject: Otherkin & Associated Groups