- a sensory experience of something that does not exist outside the mind, caused by various physical and mental disorders, or by reaction to certain toxic substances, and usually manifested as visual or auditory images.
- the sensation caused by a hallucinatory condition, or the object or scene visualized.
- a false notion, belief, or impression; illusion; delusion.
- (in the field of machine learning) false information generated by a machine learning program contrary to the intent of the user and presented as if it were true and factual.
- the alleged perception of an object when no object is present, occurring under hypnosis, in some mental disorders, etc
