It is, perhaps, not the most creative name I’ve ever come up with, but Noram is a holdover term from when the United States formed a coalition bloc with Mexico and Canada to contend with Unified Oceania and the reborn European Union in the early 2100′s. The simply named North American Bloc was abbreviated to NorAm in common speech. Long after the apocalypse, the term stuck around and everyone just assumed that’s what the land was called. Precious few people even know that there’s anywhere else to go.
The default campaign setting is dropped into North America, but nothing stops any aspiring GM from setting the game in Europe, Asia, Africa, or anywhere other than Australia. Do not go to Australia in the characters’ modern day.