More specifically, the [first/second/third world model](https://en.wikipedia.org/wiki/Third_World) is now entirely outdated, and those who refer to countries as "third world" countries are using old terminology.

The first world used to be NATO countries, the second soviet bloc, and third those who politically didn't align themselves. These tended to be less developed countries, who were typically still figuring out their own stability and didn't inject themselves into the global conversation. Now it's used as a economic classification almost.

Relevant, current terms would be MDC/LDC-- more/less developed countries.