All terms
Foundations
Hallucination
When a model states something fluent and confident but false or made up.
Definition
A hallucination is output that is plausible and confidently stated but factually wrong or fabricated — invented citations, nonexistent APIs, or incorrect facts. It stems from the model optimizing for likely-sounding text rather than truth. Mitigations include retrieval-augmented generation, tool use, and grounding answers in verifiable sources.