A FlyerTalk Posting Legend
Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 102,617
If XXX is an airport code, exXXX would mean a flight departing from XXX.
BUF-JFK could be intraUSA, just like we say intraAsia or intraEU/intraEurope, but most people would just say that it's a (USA) domestic flight.
BTW, I like to write USA rather than US for the country here to avoid confusion with US the (former) airline = USAir.