Japanese Domestic Market. The "domestic" there means that it is Japanese parts made for the Japanese market (some Americans seem to be confused and think that it means Japanese parts made for the US market.) That's parts that have to be ordered from Japan, because they were never intended for any market other than Japan. Not every Japanese part is JDM. Most people who toss the term "JDM" around are using it wrong.*DM applies to parts from and for ANY country. So you've got USDM, KDM, and...well, I guess with the EU, it would be EDM rather than individual countries, or maybe not, I'm not sure on that one.