Pan is an old-time seldom seen card game. You can still find it being played here and there.
A buy-in chip is usually won in a poker tournament qualifying game. Instead of a cash prize, you get a buy-in chip to use either as part of your buy-in for the main tournament or another qualifier. For instance, the big game in the WSOP (World Series Of Poker at Binion's this month) is a $10,000 buy-in. You can play in satellite tournaments and win $500 buy-in chips to use as entry to other WSOP satelites or the main tournament or you can sell them to others.