Price of one country's money in relation to another's. Exchange rates may be fixed or flexible. An exchange rate is fixed when two countries agree to maintain a fixed rate through the use of monetary policy. Historically, the most famous fixed exchange-rate system was the gold standard; in the late 1850s, one ounce of gold was defined as being worth 20 U.S dollars and 4 pounds sterling, resulting in an exchange rate of 5 dollars per pound. An exchange rate is flexible, or floating, when two countries agree to let international market forces determine the rate through supply and demand. The rate will fluctuate with a country's exports and imports. Most world trade currently takes place with flexible exchange rates that fluctuate within relatively fixed limits. See alsoexchange control, foreign exchange.