Hi Tim
JDM means Japanese Domestic Market, so effectively that means a car imported second-hand from Japan.
The instantly noticeable difference is the headlight washer nozzles on the bumper facing the headlights.
All UK market cars have them.
NO Japanese market car ever had them.
There are other differences. UK cars were very expensive new, and came "fully loaded" as they say in the States. Standard equipment on UK cars included glass headlights, airbag, sunroof, ABS, cruise, leather, heated front seats and so on. Of the extras just listed, the heated seats option was never offered in Japan or USA.
There are compensations to having a Japanese model. One I like is the "Power" button on the gearshift console. When pressed, this will leave the gearbox operating from the Power shift map. Hangs onto gears longer, changes down sooner for acceleration, much more sporty than the lazy standard Normal mode the UK ones have.
Also, they all have the "closing" switch on the mirrors, motorised closing. UK cars or US cars never got this option.
There are other minor differences, you will learn about them as you go along.
So which type is yours, then?
Joe