Specifically third world countries were originally defined as countries neither aligned with NATO or the Soviet Union during the Cold War. So technically this would have included Austria, Finland, Sweden, and Switzerland, but generally the term is only used to describe poor and under developed countries in Africa, Asia, and Latin America.
First and third world countries are specific countries categorized after WWII.
Specifically third world countries were originally defined as countries neither aligned with NATO or the Soviet Union during the Cold War. So technically this would have included Austria, Finland, Sweden, and Switzerland, but generally the term is only used to describe poor and under developed countries in Africa, Asia, and Latin America.
You should look into the history of it a bit, the categories were really always kinda about the skin color