For a term with such outsized importance in car culture, "JDM" is an acronym for a fairly boring phrase Japanese Domestic Market. It refers to items built and intended for sale and use within Japan.Japanese-branded enthusiast cars are often tagged as JDM despite not being strictly "JDM" in terms of their origin or original market. Beyond the actual industry definition of JDM, the term has become one of the overarching labels for Japanese car fandom worldwide, gaining far more meaning in common usage than from its original industry context.
