Perceptual Illusion: 

Multistable perception involves a stimulus that is too ambiguous for the mind to decide on a definitive interpretation. The example below, the Necker Cube, shows this phenomenon with its oscillation between two possible states. One can see a cube with its front pointing down and to the left or up and to the right. 

The image in itself is only a series of lines. The brain contextualizes it as a three dimensional object due to the angles of some of the lines. However, because there is no shading or indication of orientation, it has to make assumptions based on where one focuses.