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Both discs and players can be region-locked. You can find multi-region players, as well, but it’s important to note that most of these have been made region-free by hacking and aren’t officially endorsed by the manufacturer.
A player will identify the region code for the disc(s) and allow or prevent access. So, if you take a DVD from Region 3 and try to play it in a DVD player from Region 1, it’ll return an error. You’ll see something like “Error: Playing of this disc is prohibited in your region.” This matters for anyone looking to ditch streaming for physical media in the modern age. You’ll want to pay attention to the region numbers on DVDs you buy from private sellers, online, and at retailers.
As for how countries are organized: Region 1 is USA and Canada, Region 2 includes Japan, Europe, South Africa, Middle East and Greenland, and Region 3 covers South Korea, Taiwan, Hong Kong, and Southeast Asia. From there, under the Region 4 umbrella is Australia, New Zealand, Latin America, and Mexico, while Region 5 is Eastern Europe, Russia, India, and Africa, and finally Region 6 is China. Regions 7 and 8 are for special use cases. To avoid problems, don’t mix and match regions between discs and players, or just use a region-free player. Blu-Ray region coding is simpler, with only Region A, Region B, and Region C. A covers North America, South America, U.S. Territories, Japan, South Korea, Taiwan, and Southeast Asia, B includes Europe, Africa, Middle East, Australia, and New Zealand, while Central and South Asia (including China, India, and Russia) fall under C.
