These terms don't mean 2nd and 3rd tier countries. At least they didn't used to.
> The three-world model arose during the Cold War to define countries aligned with NATO (the First World), the Eastern Bloc (the Second World, although this term was less used), or neither (the Third World). Strictly speaking, "Third World" was a political, rather than an economic, grouping.
> The three-world model arose during the Cold War to define countries aligned with NATO (the First World), the Eastern Bloc (the Second World, although this term was less used), or neither (the Third World). Strictly speaking, "Third World" was a political, rather than an economic, grouping.
https://en.wikipedia.org/wiki/Third_World