In one sentence: A hallucination is when an AI tool says something false as if it were true.
Why it matters: The US National Institute of Standards and Technology (NIST) describes this as content that is confidently stated but wrong, and says people can be misled by the confident tone. A confident answer is not always a correct one.
One thing to do: Check one important fact from an AI answer on an official website, such as a government or company page.
Related terms: large language model, chatbot, training data
Checked: 25 Oct 2026.
