Explanation:

It refers to the dangers of over-exploitation of resources due to lack of property rights over them (‘commons’ are the resources neither owned privately nor by the state but are open for free use by all), for e.g. a community pond or Antarctica or international high seas that have been ecologically exploited by humanity.
Individual users acting independently according to their own self-interest behave contrary to the common good of all users by depleting that resource through their collective action. A rationing or imposing of levy on such resources acts as a check on their exploitation.