From Luke Jackson

Summary

DVD-Video discs may be encoded with a region code intended to restrict the area of the world in which they can be played. Discs can be produced without region coding; they are sometimes referred to as region 0 discs.

The commercial DVD player specification requires that a player to be sold in a given place must not play discs encoded for a different region (region 0 discs are not restricted). The purpose of this system is to allow motion picture studios to control the various aspects of a release (including content, date and, in particular, price) according to the region. In practice many DVD players are or can be modified to be region-free, allowing playback of all discs. Entirely independent of CSS encryption, region coding pertains to regional lockout, which originated in the video game industry.

Read more on Wikipedia about DVD_region_code

My Opinion

The Motion Picture Association of America's attempt to divide the global market into smaller more manageable markets. This is done to ensure that they can "culturalize" their propaganda for each market independently. This in theory drives more sales by launching the product multiple times in multiple locations rather than having to manage a global launch.

Mac OS X

The DVD Player Application that is included with the Mac OS X operating system supports the Motion Picture Association of America