Dark matter is defined as hypothetical matter that is undetectable by its emitted radiation, but whose presence can be inferred from gravitational effects on visible matter. It has been used in a variety of fictional elements, including computer and video games and books. In such cases, dark matter is usually attributed extraordinary physical or magical properties. Such descriptions are often inconsistent with the known properties of dark matter proposed in physics and cosmology. For example in computer games, it is often used as material for making weapons and items. Compare to exotic matter.