Definition: An abnormal perception that a visual or other sensory stimulus is there, when in reality, it isn't. For instance, if you came across a lone man in a subway station having a heated debate with someone who is not there, the man could be having a visual and/or an auditory hallucination. By definition, hallucinations happen to people who are awake and otherwise aware of their surroundings, and are common in some psychiatric and neurological conditions.
Also Known As: visual, auditory, olfactory or tactile hallucinations.
