The Rival Good vs. The Non-Rival Good
According to Wikipedia, the notion of the rival good designates a competitor in which consummation by one person prevents consummation by others (i.e. an apple can only be eaten once, generally by a single person). On the contrary, the non-rival good is one that can be simultaneously consumed by several people without causing direct loss of the good (i.e. an MP3 song can be downloaded and listened to by millions of people at the same time). The majority of such non-rival goods are often intangible. When one sells the intangible good, one still possesses it. There is therefore no exchange, but rather a duplication of the good. It was Lawrence Lessig, law professor at Stanford University and creator of the legal tool Creative Commons, who first enlightened us about the difference between the rival good and the non-rival good.