As has already been noted, a swap is a contract to exchange two income streams for example, fixed-rate and floating-rate interest on the same notional sum. Swaps are a recent invention they date only from the early 1980s but they have become important financial derivatives, widely used to manage the risks of interest-rate fluctuations. Around 47 percent of the $273 trillion in total notional amounts of derivatives contracts outstanding worldwide at the end of June 2004 was made up of interest-rate swaps.

Donald MacKenzie, An Engine, Not a Camera, loc. 979