Second World refered to nations with command economies. The first, second and third world terminologies were developed during Cold War to describe political alignments. China and Russia were both considered part of the Second World. The third world back than was non aligned nations many of them recently independent colonies that were fought over by the first and second world. Nowadays third world is just used to describe dirt poor nations.
Why, then, were non-aligned nations such as Finland, Sweden, and Switzerland still considered First World? And why were certain nations (North Vietnam, to name merely one example) who were clearly aligned on one side or the other still considered Third World?
You are generally correct in defining what Third World means today, but, even under definition, I would like to see any link indicating that Romania and Belarus and Russia are Third World nations. Mind you, even if they are, they are still part of Western Civilization. I'll get back with you in a day or two on that one.;)