Definition of "hallucination"

Hallucinations are always evidence of cerebral derangement and are common phenomena of insanity.

1871, William Alexander Hammond, A Treatise on the Diseases of the Nervous System

The authorities said that the spinach had caused “possible food-related toxic reactions” with those affected experiencing symptoms including delirium, hallucinations, blurred vision, rapid heartbeat and fever.

2022 December 18, Yan Zhuang, “How Can Tainted Spinach Cause Hallucinations?”, in The New York Times‎

This must have been the hallucination of the transcriber.

1712 September 9 (Gregorian calendar), [Joseph Addison], “FRIDAY, August 29, 1712”, in The Spectator, number 470; republished in Alexander Chalmers, editor, The Spectator; a New Edition, […], volume V, New York, N.Y.: D[aniel] Appleton & Company, 1853

Chatbots even forget that they are a bot and experience "hallucinations", Meta's description for when a bot confidently says something that is not true.

2022 August 8, Liam Tung, “Meta warns its new chatbot may forget that it's a bot”, in ZDNET‎

Hallucinations are about adhering to the truth; when A.I. systems get confused, they have a bad habit of making things up rather than admitting their difficulties.

2022 December 16, Farhad Manjoo, “ChatGPT Has a Devastating Sense of Humor”, in The New York Times‎

It may tell you that the official currency of Switzerland is the euro (it’s actually the Swiss franc) or that Mark Twain’s Celebrated Jumping Frog of Calaveras County could not only jump but talk. A.I. researchers call this generation of untruths “hallucination.”

2023 January 10, Cade Metz, “A.I. Is Becoming More Conversational. But Will It Get More Honest?”, in The New York Times‎