What is meant by "public good" in economics?

In economics, a "public good" is defined as a good that is both non-excludable and non-rivalrous. Non-excludable means that it is not possible to prevent individuals from accessing the good, regardless of whether they have paid for it or not. Non-rivalrous indicates that one person's use of the good does not diminish another person's ability to use it. Classic examples of public goods include national defense and public parks. These goods provide benefits to all individuals, and people cannot be easily excluded from using them, even if they do not contribute to the funding.

The other options reflect misconceptions or incomplete definitions of public goods. For example, a good priced lower than its demand refers to market dynamics rather than the characteristics of public goods. A good sold by public enterprises focuses more on the seller rather than the intrinsic properties of the good itself. Lastly, while many public goods do receive government funding, not all goods that require government funding are necessarily public goods; some may be private or merit goods that just require subsidies.