"Illusion is used to misguide, deceit and to confuse others. We use Illusion spells most often against Muggles to shield them from our world. The use of Illusion spells at Hogwarts are commonly used to trick teachers into forgetting homework, and sorts. Those do not work on me, I can tell you. "
Illusion, formally known as the School of Illusion, is a type of magic that is mainly used to confuse, mislead and to deceit people. Illusion is more commonly used against Muggles to shield them from the Wizarding world, although some Illusion spells have been used against Wizards.