what is an illusion?

Question

mention any three illusions and explain them

http://hlavolamy.szm.sk/brainteasers/optical-illusions-4.htm

http://www.onelook.com/?w=illusion&ls=a

So an illusion is something that people believe that is false.

Some students have the illusion that Jiska volunteers do homework for them.
The illusion was clear enough to them, and the masses blamed the Jews, and the National Socialists were viewed as saviours.
Ghosts come at night and haunt the city, during the dark and fog they appear as faint whisps in far shadows. Most of us have seen them.

Illusions exist in many places. I hope you were helped. The optical illusion site is nice.

It is better to distinguish between an illusion and a delusion.

http://www.members.cox.net/dagershaw/lol/IllusionDelusion.html

I hope this helps a little more. Thanks for asking.