What do we mean by hallucinate? I'm not counting it making a mistake that it fixes on its own without intervention. I'm no expert on the inner workings/harness

What do we mean by hallucinate? I'm not counting it making a mistake that it fixes on its own without intervention. I'm no expert on the inner workings/harnesses/etc beyond a basic understanding of the architecture. Maybe I've just developed a good sense for effective prompts? I could share some recent sessions.