This is a collection of short explanations of the commons.
# By Pat Mooney "The commons is an attitude." (my favorite one)
# By David Bollier "The commons is…. - A social system for the long-term stewardship of resources that preserves shared values and community identity. - A self-organized system by which communities manage resources (both depletable and and replenishable) with minimal or no reliance on the Market or State. - The wealth that we inherit or create together and must pass on, undiminished or enhanced, to our children. Our collective wealth includes the gifts of nature, civic infrastructure, cultural works and traditions, and knowledge. - A sector of the economy (and life!) that generates value in ways that are often taken for granted – and often jeopardized by the Market-State." [excerpt of a somewhat longer enumeration]
# Sources
Bollier: blog 
# See also commons