1: U.S., Canada, U.S. Territories
2: Japan, Europe, South Africa, and Middle East (including Egypt)
3: Southeast Asia and East Asia (including Hong Kong)
4: Australia, New Zealand, Pacific Islands, Central America, Mexico, South America, and the Caribbean
5: Eastern Europe (Former Soviet Union), Indian subcontinent, Africa, North Korea, and Mongolia
8: Special international venues (airplanes, cruise ships, etc.)
Region 7 is reserved for future assignment, if needed. It's just to give some flexibility to the system - to allow a new region (such as the moon <IMG SRC="http://peel.gotfuturama.com/ubb/smile.gif
">, for example) to be created.
Region 8 isn't pointless - movies are often available as inflight entertainment well before they are released on DVD to buy.