Hallucination refers to the perception of stimuli that are not actually present in the external environment. These altered sensory experiences can involve any of the five primary senses—such as hearing voices (auditory hallucination), seeing figures (visual hallucination), or smelling odors that do not exist (olfactory hallucination). Clinically, hallucinations are considered a symptom rather than a disease itself, and they can manifest due to various underlying causes, including metabolic imbalances, neurological damage, psychoactive substance intoxication or withdrawal, and various psychotic disorders. The phenomenon is thought to result from disruptions in the brain's neural pathways responsible for interpreting sensory input and distinguishing internal mental generation from external reality.