Illusion v.s Delusion

Recently, I am confused by 3 terms: illusion, delusion and hallucination. After doing a little "research" on web, I finally know how to distinguish one from another.

An illusion is a misleading perception, usually visual. It deals with stimuli that are actually present, but it is misinterpreted in terms of length, shapre motion or direction, or sometimes hard to interpret.

A hallucinations involve sensing something that is not actually present. It is most frequently auditory.

A delusion is a deeply held false belief that is maintained, even when other information contradicts the belief. The contradictory information is either ignored completely or discounted in some way.

In summary, an illusion is a perceptual disturbance, while a delusion is a belief disturbance.