In monetary policy, the base currency, also known as MonetaryBase, strong currency and initial currency, is also known as high power currency because it can enlarge or reduce the total money supply. It is a debt certificate issued by the central bank, which is manifested in the deposit reserve of commercial banks (R) and the currency held by the public (C). In the report of the International Monetary Fund, the base currency is called the reserve currency, which means the total amount of money printed. The base currency is the basis for the entire commercial banking system to create deposit currency, and it is the source of the multiple expansion of deposits in the entire commercial banking system.

The so-called "base currency" in foreign exchange transactions refers to the first currency in any currency pair. Exchange rate shows the geometry of the first currency to measure the value of the second currency. For example, suppose the exchange rate of USD/CHF is 1.6350, which means that 1 USD is equal to 1.6350 CHF. In the foreign exchange market, the US dollar is generally regarded as the base currency in the quotation, which means that the quotation is that all other currencies show a value of US$ 65,438 +0. The main exceptions are the pound, euro, Australian dollar and New Zealand dollar. In contrast, the quotation currency is the second currency in any currency pair, which is usually called pip currency.