They are not primitive,
underdeveloped, or poor, as many believe. A third world country is
just a country that is not considered a capitalist country (first
world) or a communist country (2nd world). The terms “first world”
and “second world” virtually disappeared from usage after the fall
of the Soviet Union.
The terminology came about just after WWII with the “first
world” countries that were aligned with the United States common
political and economic structure (capitalists). Second world
countries were those that aligned with the Soviet Union in terms
of their political and economic structure (communists and
socialists). Third world countries were the rest that were not
aligned with either, whether poor or not.
Correct term to refer to poor or underdeveloped countries is
“Developing World”.