What is the difference?
The key difference between "allusion" and "illusion" lies in their meanings and usage:
"Allusion" is a technique where the author directs the audience to make a comparative reference to other works or events. It invites the reader to make connections to something outside the work itself.
"Illusion," on the other hand, refers to something misleading or deceptive, often creating a false or threatening image or appearance.