For A expression with this sort of outsized relevance in car or truck lifestyle, "JDM" is undoubtedly an acronym for a fairly tedious phrase: Japanese Domestic Sector. It refers to things built and supposed for sale and use within Japan (i.e., not for export). This includes almost everything from automobiles https://elevemotors.com/product/nissan-gt-r-gtr-r35-v6-38-v6-benzin-vr38dett-vr38-11000-jf0ha/