Usage Form of the Commons
A good can only be used exclusively, if the access to the good is generally prevented and selectively allowed (e.g. if a „bagel“ is bought). It can be used inclusively, thus non-exclusively, if the access is possible for all people (e.g. Wikipedia). The usage of a good is rival or rivalrous, if using the good by one person restricts or prevents use options for other people (e.g. listening to music by earphones). A usage is non-rival, if this does not result in limitations for others (e.g. a physical formula).
The usage scheme is used by classical economists as the authoritative charateristic for goods. But it is far too narrow-minded. It combines two aspects which in fact occur together with usage while the causes are completely different. The exclusion is a result of an explicit activity of excluding people, thus closely linked with the social form. On the other hand, the rivalry is closely linked with the constitution of the good—indeed, an apple can only be eaten once, for the next consumption a new apple is needed. " (http://www.keimform.de/2010/01/11/commons-in-a-taxonomy-of-goods/)