在经济学上，汇率（英语：exchange rate，foreign-exchange rate，forex rate，FX rate，或Agio）定义为两国货币之间兑换的比例。通常会将某一国的货币设为基准，以此换算金额价值他国几元的货币。在英文使用方面，有时简写为FX，此为外国货币Foreign Exchange的简写。

通俗地说，汇率是一国货币单位兑换他国货币单位的比率，也可以说是用一国货币表示的另一国货币的价格。

汇率的特性在于它多半是浮动的比率。只要货币能够透过汇率自由交换，依交换量的多寡，就会影响隔天的汇率，因此，有人也以赚汇差营利，今日以较低的比率购进某一外币，隔日等到较高的比率出现时，再转手卖出。

In finance, an exchange rate (also known as a foreign-exchange rate, forex rate, FX rate or Agio) between two currencies is the rate at which one currency will be exchanged for another. It is also regarded as the value of one country’s currency in terms of another currency. For example, an interbank exchange rate of 119 Japanese yen (JPY, ¥) to the United States dollar (US$) means that ¥119 will be exchanged for each US$1 or that US$1 will be exchanged for each ¥119. In this case it is said that the price of a dollar in terms of yen is ¥119, or equivalently that the price of a yen in terms of dollars is $1/119.