DVD Regions are restrictions encoded onto a DVD that determine where in the world it can be played. Hong Kong belongs to region code 3.
The purpose of DVD Regions is to allow motion picture studios to control several aspects of their DVD movie releases, including content, release date, and price.
DVD players are formatted to only play DVDs with your region code. In other words, you will not be able to watch a DVD with a region code that is not your own, which in most cases is not a problem.