An **illusion** is a distortion of the senses, revealing how the brain normally organizes and interprets sensory stimulation. While illusions distort reality, they are generally shared by most people. Illusions may occur with more of the human senses than vision, but visual illusions, optical illusions, are the most well known and understood. The emphasis on visual illusions occurs because vision often dominates the other senses.
A **delusion** is a belief held with strong conviction despite superior evidence to the contrary. Unlike hallucinations, delusions are always pathological (the result of an illness or illness process). As a pathology, it is distinct from a belief based on false or incomplete information, confabulation, dogma, illusion, or other effects of perception.