First, Second, Third and Fourth World
I've always meant to look this stuff up. I hear the terms all the time and only guessed what they meant. It turns out I wasn't that far off.
First World: Basically those countries first in NATO.
Second World: Those in the initial Warsaw Pact.
Third World: Countries that didn't fit in the other two.
Fourth World: The modern countries that still have no industrial infrastructure. I suppose these countries are in the agricultural age, only with AK-47s and RPGs.