Japanese domestic market, anything that comes from japan is jdm, jdm car parts arent set up to conform to all the laws in the US, they were built only for use in japan and misc countries allowing it, they are oem parts the way they were ment to be with better engineering.
i dont know if this is true or not but i heard they are cheaper because in japan a car only gets about give or take 50k miles on them before they cant pass emissions, then they are stripped for parts and sent to the US, and they are so plentifull they sell cheap. but be carfull, 50k miles in japan might be like having 250k miles in the US because its tedious stop and go driving. a depending the area the car came from a 45min drive for them could be less than 10 miles