What is a defining characteristic of a public good?

A defining characteristic of a public good is that it is non-excludable and non-rivalrous in consumption. Non-excludability means that once the good is provided, individuals cannot be prevented from using it, making it accessible to all. Non-rivalry indicates that one person’s consumption of the good does not diminish the ability of others to consume it as well. A classic example is national defense: everyone benefits from it, and one person's benefit does not reduce the level of protection available to others. This characteristic distinguishes public goods from private goods, where consumption is limited and one individual's use can hinder another's access.