---
title: "Hallucination: Definition"
description: "A fluent but false or unsupported output from a language model. Mitigated by grounding, guardrails, evals and human review rather than eliminated."
canonical: https://sudosapient.si/terms/hallucination
updated: 2026-10-27
publisher: Sudo Sapient (https://sudosapient.com/)
---
# Hallucination

**Hallucination:** A fluent but false or unsupported output from a language model. Mitigated by grounding, guardrails, evals and human review rather than eliminated.

## Why it matters

Hallucinations cannot be eliminated by prompting alone, so production systems are designed around them: grounding answers in retrieved sources, validating structured outputs in code, using confidence thresholds, and routing uncertain cases to people. Measuring the hallucination rate on an eval set is the only way to know whether changes help.

## Related terms

- [Grounding](https://sudosapient.si/terms/grounding): Constraining an AI model's output to verifiable source material, such as retrieved documents or database records, to reduce unsupported claims.
- [Guardrails](https://sudosapient.si/terms/guardrails): Deterministic checks and limits around an AI model, such as schema validation, thresholds, allow-lists and approval gates, that prevent or catch harmful or invalid outputs.

## Where it comes up

- [What Is AI Transformation? A Plain-English Definition for Operators](https://sudosapient.si/entries/what-is-ai-transformation)

## In practice

Every Sudo Sapient build ships with this in place before go-live, because it is part of what separates a demo from a production system. [See how the studio works](https://sudosapient.com/).