Second World" refers to the (former) communist-socialist, industrial states, (formerly the Eastern bloc, the territory and sphere of influence of the Union of Soviet Socialists Republic) today: Russia, Eastern Europe (e.g., Poland) and some of the Turk States (e.g., Kazakhstan) as well as China.
"Third World" are all the other countries, today often used to roughly describe the developing countries of Africa, Asia and Latin America.
The term Third World includes as well capitalist (e.g., Venezuela) and communist (e.g., North Korea) countries as very rich (e.g., Saudi Arabia) and very poor (e.g., Mali) countries."

http://www.nationsonline.org/oneworld/thir...d_countries.htm
Vietnam is listed as Thirdworld and also a second world nation (see note)
Third worll can be very rich and also very poor