A public good is a commodity or service that is non-excludable (no one can be effectively excluded from using it) and non-rivalrous (one person's use of the goo

A public good is a commodity or service that is non-excludable (no one can be effectively excluded from using it) and non-rivalrous (one person's use of the good does not reduce its availability to others) Examples include clean air, national defense, and public parks. This isn't to say they shouldn't be provided by the government, but they're definitely not a public good