Define and give an example of a public good. can the private market provide this good on its own? explain

A public good is a good which is non-excludable (you can't keep people from partaking in the benefits of its existence) and non-rival (my partaking in the good does not interfere with yours). Because of external effects, private decisions about consumption and production can lead to an inefficient allocation of resources, and government intervention can potentially raise economic well-being.