Certain nations were categorized as Third World countries in the last half of the 20th century. This is now considered an outdated and derogatory phrase used to describe nations that were economically underdeveloped and had little or no affiliation with major world powers.

The Third World countries occupied one of four segments that identified nations by their relative economic standing. Roughly, the major world powers and their economic and political allies were First World countries, allies of the Soviet Union were Second World countries, underdeveloped nations were Third World countries, and nations that were entirely isolated from global politics and economics were the Fourth World.