The traditional theoretical concept of public goods does not distinguish with regard to the geographical region in which a good may be produced or consumed. However, the term "global public good" has been used to mean a public good which is non-rivalrous and non-excludable throughout the whole world, as opposed to a public good which exists in just one national area. Knowledge has been used as a classic example of a global public good. In some academic literature, it has become associated with the concept of a common heritage of mankind.