Exchange rate is also called exchange rate, foreign exchange quotation or foreign exchange market, that is, the buying and selling price of foreign exchange. It is the relative price of two countries' currencies, that is, the price of one country's currency is expressed in another country's currency.

Under different monetary systems, there are different ways to set the exchange rate. Under the gold standard, due to the different gold contents of currencies in different countries, the comparison of the gold contents of the two currencies (also called coinage parity) is the basis of foreign exchange rate. Under the dishonoured credit currency system, exchange rate changes are restricted by the relationship between foreign exchange supply and demand. When a currency is in short supply, its exchange rate will rise, and when a currency is in short supply, its exchange rate will fall.