When a currency provides a basis of exchanged rates for international transactions, this type of currency is referred to as a key currency. A currency that remains stable and unfluctuating is also a factor for referring to it as a key currency. They set the pace for other types of currencies because of their wide usage as a global currency. Another criterion that allows any country's currency to be used as a key currency is it's strong economic and financial background, also being a player in the global market. Key currency has a better valuation when we talk about currency valuation stability.
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