“Illusion: The semblance of reality and verisimilitude (q.v.) in art which most writers seek to create in order to enable the reader to think that he is seeing, feeling, hearing, tasting and smelling, or, conceivable, having some extra-sensory or kinesthetic experience. The creation of illusion is a cooperative act between writer and reader. It brings about in the reader what Coleridge called “the willing suspension of disbelief” (q.v.). However, the writer also destroys illusion, sometimes for a specific purpose: for example, to address the reader directly—a not uncommon practice among 18th and 19th century novelists. The contrast helps the illusion and at the same time sharpens and clarifies the impression of things happening at a distance. Illusion should be distinguished from delusion and hallucination.”
Excerpted from: Cuddon, J.A. The Penguin Dictionary of Literary Terms and Literary Theory. New York: Penguin, 1992.