A term used to describe situations in which there is a “commons” (a resource without rules governing use) which suffers overuse (because individuals have no incentive to conserve). Contrast with CornucopiaOfTheCommons.
Imagine a pasture which is governed by no law or owner. Any individual or group can let any number of cows graze upon this pasture.
If the total number of cows is small enough, there is no problem. But if the total number of animals is large enough, so that the plants in the commons are eaten faster than they regrow, then eventually the commons will be destroyed from overuse. Sadly, each individual has more of an incentive to let their animals graze as much as possible than they have an incentive to conserve.
This is an argument for governance or private property. If the commons has a government, then the situation is improved, because the society has an interest in preventing overuse. And if the commons has an owner, then it is in the owner’s interest to prevent overuse.
The paper does not prefer a government to an owner, or an owner to a government. Commons does not mean “communal resource,” because communal resources that are communaly governed are secure: Individuals can only bring so many cows, and when the cows nears dangerous numbers, the government policy is applied to preserve the pasture.
I believe the article has been mis-interpreted by Libertarians, and private property advocates.
The last point is the most interesting to me: The article is using the word “commons” in a way that is dramatically different than what we intuit by the word “commons.”
Roads are commons. Trash dumps are commons. Air is a commons. But none of these are commons in the author’s sense of the word! By the authors sense of the word, these are not commons, because they are governed.
I strongly believe, after reading the full article, is that the word “commons” was poorly chosen. He should have used the word “lawless,” instead.
I can understand the mistake- he meant “things that are like everybody’s private property, where you can do whatever you want with it.” Note that this excludes roads, since you have to obey the laws of the road. Note that this excludes trash and dump sites, which are governed and managed. Note that this excludes air, because air polution is also managed, regulated, monitored. None of those are commons, by the author’s use of the word.
So, in conclusion: I believe the article should be called: “TheTragedyOfLawlessness?.”
But that is an obvious point.
I just read the Wikipedia article on the Tragedy of the commons, and found that my thoughts on this are not new. 
This quote from that wikipedia article reminds me of http://www.benkler.org/CoasesPenguin.html
A popular solution to the problem is also the “Coasian” one, where the individuals using the commons make payments to one another in exchange for not overusing the resource.