What is a Tulpa?

(Adapted from my blog and the /r/Tulpas wiki.)

While everyone has their own interpretation, this is a common definition of a tulpa cited by most guides, FAQs, and glossaries:

"A tulpa is an autonomous entity existing within the mind of its creator, the host. It is distinct from the host in that it possesses its own personality, opinions, and actions, which are independent of the host’s. A fully-formed tulpa is, or highly resembles to an indistinguishable point, an actual other, sentient consciousness coinhabiting with the host mind.
They are willingly created by people via a number of techniques to act as companions, muses, and advisers."

Put simply, a tulpa is a sentient imaginary friend. The key difference is that, unlike the classic idea of an imaginary friend, a tulpa does not do exactly what its creator wants it to do. A tulpa possesses independent thought processes and forms its own opinions. This is generally taken as the mark of sentience in the tulpa community. That said, the definition of sentience is disputed and varies, both within the tulpa community and in general.

Tulpas are NOT a replacement for human social contact, but a means of personal insight, improved perspective, and companionship outside of a usual social life. While some may seek to use a tulpa in lieu of a social life and a wonderland instead of experiencing reality, it is highly discouraged within the community. A tulpa should not be used to escape life, but to enhance it.

Ultimately, each tulpa is unique and distinct to the mind of their creator and host, so while we can assert generalities, specifying exactly the how and why of tulpa is beyond our current capabilities.

Long story short:

-A tulpa is:
> An autonomous, sentient entity (or at least one that strongly appears sentient), widely regarded as psychological in nature, that coinhabits a body and brain with its creator (the host)
> Manifested from unconscious agents (more widely known as intuition, gut feelings, the voice in the back of the head, the angel on the shoulder) within the host’s deeper personality
> Created by the host for companionship, assistance with a task, or some other purpose
> Capable of, or at least strongly appearing capable of, possessing its own thoughts, feelings, beliefs, and actions, which can differ from the host’s

-A tulpa is NOT:
> Role-playing. Regardless of whether tulpas are truly sentient or not, tulpamancers experience their tulpas as very real presences and are not making their experiences up.
> A replacement for physical social relationships or a means to escape from reality.
> Malicious by nature. While malicious tulpas do exist, they are far and away the minority; the majority of tulpas are, in fact, very friendly and helpful to their hosts.
> Self-induced DID, schizophrenia, or any other sort of mental illness. The hallmark of a mental illness is that it is disruptive, destructive, and uncontrollable—tulpamancy in itself is a neutral and highly controlled process, and the majority of tulpamancers live normal lives or even are positively influenced by their tulpas.
> Likewise, tulpamancy is NOT an attempt to downplay the seriousness of DID, schizophrenia, or other mental illnesses. The vast majority of tulpamancers do not regard themselves as having DID or schizophrenia. We believe tulpamancy to be distinct from DID, and regard mental illness as a serious issue.

For further reading:
/r/Tulpas on "What is a tulpa?"
Essays by Falunel on tulpamancy
Progress of a scientific study on tulpamancy