Definition: An erroneous mental representation, Delusion (the act of deluding), Deception by creating illusory ideas.
These below pictures are illusions stimulating our nerves in making some confusion by our eyes.
Illusion 1
Illusion 2
Illusion 3
Illusion 4
Illusion 5
Illusion 6
Illusion 7
Illusion 8
Illusion 9
I am sure that you would have worked out all of them well, as they are just illusions. It's just for fun.