What does hallucination mean?
A hallucination is an experience or idea that appears real but lacks an appropriate basis in the outside world. In psychology and medicine, the term most often refers to a false perception: a person may see an object that is absent, hear a voice no one else can hear, or feel a sensation without a physical cause. Such experiences can arise from illness, medication, sleep, intense stress, or other conditions, although they are not automatically evidence of serious mental illness. More broadly, hallucination means a mistaken idea or assertion presented as fact. This figurative use has become especially common when discussing errors generated by artificial-intelligence systems. The word's history reflects its association with a wandering mind: it comes from Latin, where the related verb referred to wandering or being lost in thought. Its strong connotation of something vividly perceived but unreal makes it useful for describing both unusual perceptual experiences and serious failures of accuracy or judgment.
nounA false perception or apparent experience occurring without an appropriate external stimulus. More broadly, it can refer to a mistaken idea or representation presented as real, especially in discussions of belief, language, or artificial intelligence.
- A false sensory experience, such as seeing, hearing, feeling, smelling, or tasting something without an appropriate external stimulus.
- A false or mistaken idea, statement, or impression presented as reality, especially in figurative, technological, or informational contexts.
"The doctor explained that the flashes of light were a visual hallucination caused by the medication."
"She knew the voices were an auditory hallucination, but they still sounded convincingly real."
"The report contained several factual hallucinations that made its conclusions unreliable."
The regular plural is used for individual false perceptions, false beliefs, or instances of mistaken or fabricated information.
"The study documented auditory hallucinations in several of the participants."
The word comes from a Latin idea of wandering in the mind: imagination and hallucination share roots in the mind's capacity to create what is not there.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does hallucination come from?
Hallucination entered English in the early 17th century from Latin hallucination, a noun formed from hallucinari, meaning to wander or be lost in the mind. The Latin word is related to Greek aluein, meaning to be beside oneself. English later developed the closely related forms hallucinate and hallucinatory, while hallucinogen and hallucinogenic refer to substances capable of producing altered perception or hallucinations.
Related word forms
How hallucination is actually used
In clinical and psychological contexts, the word usually denotes a perceptual experience rather than merely an error or falsehood. In general and technological contexts, it can describe a confidently stated but false idea, including an incorrect or fabricated output produced by an AI system.
Easily confused with hallucination
A hallucination is a perception without a corresponding external stimulus, whereas an illusion involves misperceiving something that is actually present.
A hallucination is chiefly an abnormal perceptual experience, while a delusion is a fixed false belief; the two can occur together.