Managed currency refers to a type of exchange rate system where the country's central bank intervenes in the foreign exchange market to influence the value of its currency. There are various synonyms for managed currency, including adjustable peg, dirty float, crawling peg, and flexible exchange rate. The adjustable peg system was once popular but is now uncommon, allowing countries to devalue and revalue their currencies within a certain range. A dirty float system is where exchange rates are allowed to move freely within a determined range, but the central bank can intervene to control excessive fluctuations. A crawling peg system is where a country's currency is adjusted in small increments relative to a benchmark currency. Finally, flexible exchange rates allow the market forces of supply and demand to determine the value of a currency.