Cash refers to free transactions in the international financial market, also known as "free foreign exchange". Foreign exchange widely used in international settlement and payment and freely convertible into other countries' currencies. In countries that issue these currencies, foreign exchange control and control are loose, and some even basically cancel foreign exchange control, while others have strict foreign exchange control, so their currencies cannot be freely converted into internationally used foreign currencies.

According to Article 8 of the Agreement of the International Monetary Fund, as a general obligation of member countries, a country's currency must meet three conditions before it can become a cash exchange:

1. There are no restrictions on the current account (trade and non-trade payments) and capital transfer in China's balance of payments.

2. Don't take discriminatory monetary measures or multi-currency exchange rates.

3. At the request of another member state, it is obliged to buy back the remaining domestic currency in the current account of the other party at any time.

A freely convertible currency is widely used in international exchange settlement, freely traded in the international financial market, and freely convertible into the currencies of other countries. In international trade, the import and export trade settled in these freely convertible currencies is called spot trade.