USDM
From OpenECU
Unitied States Domestic Market
Used to designate a car model that is built specifically to be sold in the United States, or possibly all of North America.
Safety requiments, emissions requirements, and market conditions (i.e. what feature buyers will buy) vary from market to market, so car manufacturers will tailor the car to meet the needs.
Other markets include JDM (Japanese) and EDM (European).