This fact might come as a shock to some.
Currently, proper definition that stands for the outdated term ‘Third World’, comes from the nature of a country’s political alignment during the Cold War; when ‘Third World’ was used to define the non-aligned countries. Switzerland was one among them.
First World: the United States, United Kingdom and its allies.
Second World: the Soviet Union, China, and their allies.
Third World: neutral and non-aligned countries.
During that time, most of the poor African countries were non-aligned; thus, the term later became popular, perhaps through internet pop-culture, and came to be known (Correctly or Incorrectly) for defining the backward economic status of a nation.
Dumbed down to,
First World: Rich countries.
Third World: Poor countries.