Hallucination
When an AI confidently makes up false information, presenting it as a fact.
In Plain English
A hallucination happens because AI does not actually "know" facts; it only knows how to predict words that sound correct. It is like a student who did not study for a test but writes a highly convincing, completely made-up essay. The AI is trying so hard to be helpful that it invents a plausible-sounding lie. This is why you should always double-check important facts generated by AI.
Real-World Example
Asking an AI for a biography of a real local politician, and the AI invents a fake college degree for them.