describes a country that doesn’t quite align with Western ideology or the Western image of society. (Also common are terms such as “third-world” (adj.), “first-world”, “developing/developed nations”, etc.)
“Three worlds” terminology originally arose during the cold war to define countries that were aligned with North Atlantic Treaty Organization (NATO) (“1st world”), aligned with the Warsaw Pact (“2nd world”), or non-aligned (“3rd world”). Because many third-world countries were economically poor, it became common to refer to poor countries as third-world.
First off, the term is archaic and refers to a /NATO vs The Communists/ worldview that is no longer relevant. Secondly, and more importantly, it presupposes a hierarchy between countries, ranked by Western ideals and homogeneity. Western ideology is a fairly narrow way to perceive global socioeconomics. In the words of Zeeshan Aleem: “Social democracy in Scandinavia, oil-funded theocracy in Saudi Arabia, and a one-party, partially planned, partially free market economy in China are all vastly different models for generating and harnessing prosperity.”
This language is wrought in Western or American/Anglo-centric worldview. It treats any country, region, or culture that didn't or doesn't follow the Western ideal of "progress" or "development", et al., as lesser. It lacks context and is dehumanizing to those people.
Be more specific or contextual. If we mean “countries with high infant mortality rates”, or “countries experiencing an HIV/AIDS outbreak”, we probably ought to say that. It’s much more clear to be specific. Further, consider the context of what we replace the phrase with — are we still imposing Western/colonialist values with our language?)