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What is Hallucination?

Updated July 21, 2026 · by Pedro

A hallucination is fabricated content presented as fact. Vague prompts increase hallucinations because the model fills missing specs. Explicit constraints reduce invented APIs and fake hex colors.

Why does this term matter for AI prompts?

Precise vocabulary reduces vague instructions. When you name hallucination correctly in a brief, Claude, Cursor, and GPT spend fewer tokens guessing. Pair definitions with structure on AI prompt builder and cost math on prompt token cost.

More glossary terms

Full list: prompt engineering glossary.

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