Tagalog, roughly translated as "coming-home gift".
The Filipino tradition, when on a trip, to buy lots and lots of stuff for people back home. You MUST make sure everybody gets something, even if it's just a bag of M&Ms for the kids, or some Hershey's bars. Pasalubong refers to both the practice and the gift itself.
Pasalubong usually consists of food products, the more exotic, the better. If you take a trip to Los Banos, for instance, you'd better bring back lots of espasol and buko pie. A vacation in Baguio would mean you'll come back loaded with strawberry jam and peanut brittle. If you're coming home late from the office, you'd better stop at the store to buy a siopao for the missus.
Foreign trips are no exception, especially trips to the US. Usual pasalubong from the US includes shoes, electronics, and whatever you can stuff into a balikbayan box. Basically, anything you can find at a duty-free shop.
It works both ways, though. Pinoys leaving for foreign shores must bring something for the folks there, and so they pack great amounts of dried mango, patis, and the reason why many first-time Pinoy travelers get chased by the drug-detection dogs at Customs - bagoong.