The price at which one currency is bought or sold in terms of other currencies, gold, or accounting units such as the special drawing right (SDR) of the International Monetary Fund. Exchange rates may be fixed by international agreement or by government policy; or they may be wholly or partly allowed to “float” (that is, find their own level) in world currency markets.
Central banks, as large holders of foreign currency, often intervene to buy or sell particular currencies in an effort to maintain some stability in exchange rates.
Under the Reagan administration, the US dollar was allowed, even encouraged, to drop in relation to other currencies, especially the Japanese yen.