Commons are any sets of resources that a community recognises as being accessible to any member of that community. The nature of commons is different in different communities, but they often include cultural resources and natural resources. An example of a cultural resource is a place "where everybody knows your name" (as in the TV program, Cheers); Ref. the book "The Great Good Place" by Ray Oldenburg.
The most widespread instance of a common is the public right-of-way, a.k.a. public roads.
While commons are generally seen as a system opposed to private property, the ideas have been combined in the idea of "common property", which are resources "owned" equally by every member of the community, even though the community recognises that only a limited number of members may use the resource at any given time.
The act of transferring resources from the commons to individual ownership is known as "enclosure."
The commons in English common-law (History)