Sort of an icon or being you build in your mind and grant power by letting live in your mind.

A tulpa is a type of supplemental consciousness capable of independent thought and with its own sense of self. It is created, intentionally or otherwise, by an existing consciousness within the same brain it comes to inhabit.

Yes, we are acutely aware that it sounds like preposterous pseudoscientific bullshit. We're just describing the concept, not expecting you to put any stock in it. We know what community we're commenting in.

The LLM in this example is not a tulpa. It only (poorly) mimics the appearance of independent thought and a sense of self, and runs on an external device.