As per Wikipedia, an optical illusion is an illusion caused by the visual system and characterized by visually perceived images that differ from objective reality. To break it further into simple words, the thing you see in an optical illusion is not what it actually is. Optical illusions have been in existence for a very long time.
A magician or an illusionist uses an optical illusion to entertain his/her audience. At times these illusions are easy to understand, while at others, they leave your mind confused.
Here is a list of 15 Optical illusions which will confuse your mind to the very core:
1.A park or a 3D globe?