An illusion is something that you see which is not real, instead the act distorts your senses into believing something that is not really true. Magicians are also referred to as illusionists because they are the masters of the art of deception. You may be under the illusion that someone loves you when they don't, or that you will inherit a fortune when you won't. Illusion quotes can describe the various ways that the mind can play tricks. Sometimes an illusion is fun or entertaining, at other times it may be frightening or disturbing, but it is always based on some sort of stimulation. That is what separates an illusion from a hallucination. When there is no stimulus then you are hallucinating and there is no illusion.