JDM: It means "Japanese Domestic Market", i.e., vehicles and components built by Japanese companies for sale and use in Japan. It does not mean "Japanese-spec", "cool", "excellent", "superior", or anything else. And the "D"-for-Domestic part is important, too. There are JDM Subarus, Hondas, Toyotas, Nissans, and Mitsubishis, but although Chevrolets and BMWs and Mercedes and Chryslers are available in Japan, none of them are JDM; they're all Japanese-market items. Likewise, there's nothing such as an "EDM" or "USDM" Honda or Toyota or Subaru.
Repo: It means "repossessed" or "repossession". It does not mean reproduction, which is sometimes shortened to repro or, for some bizarre reason, "repop".
Side markers: are at the front and rear of both sides of each vehicle first sold or imported into the US or Canada since 1/1/68. The turn signal flashers located behind each front wheel, required virtually everywhere outside North America and increasingly present on North American vehicles, are side turn signals or, more commonly, repeaters.