When you start asking around about how A.I.G. made money during the housing bubble, you hear the same two phrases again and again: “regulatory arbitrage” and “ratings arbitrage.” The word “arbitrage” usually means taking advantage of a price differential between two securities — a bond and stock of the same company, for instance — that are related in some way. When the word is used to describe A.I.G.’s actions, however, it means something entirely different. It means taking advantage of a loophole in the rules. A less polite but perhaps more accurate term would be “scam.”