The people saying it's schizophrenia are partially right.
ORIGINALLY, a tulpa thoughtform, a construct made by a meditation technique that let's you fool your brain into believing an object is real.
The point was to prove through an experiment that your perception is indistinguishable from reality, therefore proving that the Zen doctrine that reality is an illusion is true.
The idea being "if this object I created isn't real yet it seems real, then everything else that seems real might be fake too."
Pretty brilliant when you think about it.
However, a bunch of autists on the internet decided to try and use it to make imaginary friends (something the monks never intended this technique to be used for) and basically keep giving themselves mental problems in doing so.
It pisses me off that this brilliant experiment made by monks centuries ago is now reduced to this, and that when people think "tulpa" they think of you fucking idiots destroying you mental health.