For Your expression with this kind of outsized relevance in motor vehicle society, "JDM" is really an acronym for a reasonably monotonous phrase: Japanese Domestic Market. It refers to things built and supposed for sale and use inside Japan (i.e., not for export). This involves all the things from cars https://elevemotors.com/product/chevrolet-camaro-ls-16-20-oem-2-0l-turbo-engine-motor/