A person or organization who benefits from a public good but neither provides it nor contributes to the cost of collective provision. They thus free ride on the efforts of others. The free-rider problem means private provision leads to undersupply of a public good. This suggests a role for the government in public good provision. The same problem occurs internationally, when governments prefer to leave others to bear the costs of international institutions to maintain world security, and the expensive measures needed to restrain global warming or reduce destruction of the ozone layer.
Reference: Oxford Press Dictonary of Economics, 5th edt.