DVDs can be region coded so that a US made DVD cannot be played in Asia, Europe etc. There are currently 6 regions, such codes are established to allow titles to be distributed in different parts of the world at different times. This is a good option if you plan to have a release for North America, and another release for the same title in Europe or Asia countries. So people can only purchase the DVD that is made for that region The region code needs to be added at the authoring stage, and cannot be apply afterwards 

Current region codes:

(1) North America

(2) Japan, Western Europe, South Africa, Turkey and the Middle East

(3) Southeast Asia

(4) Australia, New Zealand, South and Central America and the South Pacific

(5) Northwest Asia, Russia, Indian Subcontinent and most of Asia

(6) China and Tibet

(7)Reserved

(8) Special nontheatrical venues (airplanes, cruise ships).