ELI5: Explain Like I'm 5

Optical illusion

An optical illusion is when your eyes see something that is not really there or a trick that makes your eyes think something is a different size, shape, or color than it really is. An example of an optical illusion is a picture that shows an impossible triangle! It looks like a triangle, but its sides are impossible to connect together. When you look at an optical illusion, your eyes and brain can be tricked by what they see.