Cudos to tarkill for such a detailed and correct answer :-)
Since not many people outside of airline circles (no pun intended) understand airport codes, here's a quick "translation" so to speak.
BOS Boston, MA (Logan International)
ORD Chicago, IL (O' Hare International, not to be confused with Chicago Midway, which is MDW)
BWI Baltimore, MD (Baltimore/Washington International)
PVD Providence, RI (TF Green State Airport)
LAS Las Vegas, NV (Mc Carran International)
EWR Newark, NJ (Newark Liberty International)