In the accompanying figure a white equilateral triangle is perceived, but in fact none is drawn. This effect is known as a subjective or illusory contour. Also, the nonexistent white triangle appears to be brighter than the surrounding area, but in fact it has the same brightness as the background.
The term illusory motion, also known as motion illusion, is used to define the appearance of movement in a static image. This is an optical illusion in which a static image appears to be moving due to the cognitive effects of interacting color contrasts and shape position.
This is the famous Penrose Triangle, also known as the Impossible Triangle. Though it is something that most of us have seen before, it is always cool to see how easily our brains are fooled, even when we know that it is an illusion.