Non-Exclusionary: Non-exclusionary refers to goods or services that cannot be restricted from use by individuals. For example, public parks are non-exclusionary because anyone can enter and use them freely.
Non-Rivalrous: Non-rivalrous refers to goods or services where one person's consumption does not reduce its availability for others. An example is national defense - if one person is protected by it, it doesn't mean there is less protection available for others.
Free Rider Problem: The free rider problem occurs when individuals benefit from a public good without contributing towards its provision. It arises because people can enjoy the benefits of a public good even if they don't pay for it directly.