https://www.law.cornell.edu/uscode/text/50/4302

It’s pretty clearly defined.

The word “enemy,” as used herein, shall be deemed to mean, for the purposes of such trading and of this chapter— (a) Any individual, partnership, or other body of individuals, of any nationality, resident within the territory (including that occupied by the military and naval forces) of any nation with which the United States is at war, or resident outside the United States and doing business within such territory, and any corporation incorporated within such territory of any nation with which the United States is at war or incorporated within any country other than the United States and doing business within such territory.