• The P2P Foundation offers an extensive article on the definition, meaning and etymology of the term “commons”.
• Wikipedia on commons has a more restricted view.
• Commoners Co-op offers a short helpful view: A Definition of the Commons

My own synthesis, mostly in line with what has been published by David Bollier and Silke Helfrich is that a commons implies

• a shared, valued or valuable resource (of any kind, material or immaterial)
• a community of people (commoners) who collectively use or work with that resource, and who also either own, or govern, or steward that resource
• structures, conventions, rules etc. agreed within the community by which the members of the community govern or steward the resource

They were and are at pains to point out that there are no commons without commoning.

Elinor Ostrom set out the principles that appear to be key to effective material commons.

• here they are set out concisely on the “Patterns of Commoning” site.

Commoning is then the process and/or practice of setting up and curating, governing or stewarding that resource. There is a risk that talking about commons, without explicitly including commoning, passes over the vital aspect of how the commons are set up and run. This view casts some doubt on whether the “creative commons” is referring to a commons in this sense. I would say, not.

• narrower→ a knowledge commons is a particular variety of commons with particular characteristics that distinguish it from a physical commons.