Devaluation is a reuction in the value of a currency with respect to other monetary units. In common modern usage, it specifically implies an official lowering of the value of a country's currency within a fixed exchange rate system, by which the monetary authority formally sets a new fixed rate with respect to a foreign reference currency. In contrast, (currency) depreciation is most often used for the unofficial decrease in the exchange rate in a floating exchange rate system. The opposite of devaluation is called revaluation.