I have heard of 3rd world countries, but I have never heard any mentions of 1st and 2nd world countries. There are are LDCs or Least Developed Countries. There are developing countries. There are under-developed countries. All probably meaning the same thing. There are developed countries. There are G7 countries (some say G8, with Russia, but in my opinion, Russia really does not belong there). There are OECD countries. Blah blah blah. But no, I have never heard of 1st world countries or 2nd world countries.