American internet is garbage, as others have already pointed out.
The term "third world country" is outdated, inaccurate, and usually offensive. It often comes off as racist, even if that's not intentional. Try to avoid using it unless you're sure it's appropriate (it almost never is).

What that designation OFFICIALLY meant is that the country remained neutral during the Cold War. That's all! The "First World" countries were NATO allies and the "Second World" countries were the other side led by the Soviet Union. The implication is that the countries that didn't pick a side in the Cold War were underdeveloped (which is a flawed assumption, but it was partially correct AT THE TIME).

More recently, the term has become synonymous with "poor" countries, usually those filled with non-white people. Which is dumb, because plenty of the first- and second-world countries WERE and ARE very poor. And some countries that WERE under-developed during the Cold War have since become more developed. India is the most obvious example, it's surpassing China in a lot of population+economic metrics now.

tl;dr "third world country" is a designation that's not only offensive; it's outdated, inaccurate, and dumb.