Therianthropy
In psychiatry, clinical lycanthropy is a mental disorder where a human being believes they are physically a member of a non-human species of animal. In folklore, lycanthropy is the ability to transform physically into animal form. Often, lycanthropy is used as a synonym for therianthropy.
Therianthropy is a spiritual concept in which the individual believes they have the spirit or soul, in whole or in part, of a non-human animal.
Spiritual therianthropy is not the same as lycanthropy, aka clinical lycanthropy, a mental disorder in which an individual believes they are physically of another species. While therianthropes believe they can take on the mindset of their other side, often with uncanny accuracy, in what is referred to as a "mental shift", the individual retains control and is no danger to him/herself or others. In addition, no seriously regarded therianthrope claims to be able to physically transform. In fact, many therianthropes deny that such a thing could ever be possible, mostly on scientific grounds. Unlike those who have clinical lycanthropy, therianthropes are perfectly able to function in society, with individuals who have productive careers in the US military, in the computer industry, as white-collar office workers, as artists, and even a small handful of scientists (mostly biologists, unsurprisingly).
Therianthropy does not have any central dogma or tenents, nor any recognized authority. However, there is a strong, though ill-defined notion that a therianthrope is one who feels they are the animal inside, rather than an external connection such as a totem or spirit guide, and those who claim external connections as therianthropy are sometimes shunned as fakers. Additionally, those who have been around for a long time are generally listened to, though less out of any perceived spiritual authority than simple acknolwedgement of experience.
While there is no offline social organization, there exists an online community composed of individuals who feel they are an animal inside, and who have many diverse outlooks on the concept, ranging from Christians to Pagans to a few atheist therianthropes (who hold that the explanation is psychological in nature). As could be expected, disagreements are frequent, and the many online forums and chatrooms of the community each have their own "atmosphere" ranging from total acceptance to scornful cynicism. There have been intermittent real-world gatherings, referred to as "howls", but their purpose is primarily social.
Therianthropy should not be confused with the furry fandom, though some intermixing of the groups does occur. As a rule, therianthropes are more focused on the spiritual connection to the animal within, while furries are focused on art and role-playing of anthropomorphic animals, though many therians are interested in such as well, and some furries are spiritual.