### Instruction: What is exchange rate?
### Input: In finance, an exchange rate is the rate at which one currency will be exchanged for another currency. Currencies are most commonly national currencies, but may be sub-national as in the case of Hong Kong or supra-national as in the case of the euro.
### Response: Exchange rate is the rate at which one currency will be exchanged at for another currency. Most countries have their own national currency. However, some currency are sub-national such as Hong Kong; some are supra-national such as the euro.