From the Document: "The U.S. dollar is the world's dominant reserve currency, among other such currencies including the euro, the yen, the pound, the renminbi (RMB), the Canadian dollar, the Swiss franc, and the Australian dollar. A reserve currency is a currency held by central banks in significant quantities. It is widely used to conduct international trade and financial transactions, eliminating the costs of settling transactions involving different currencies. The dollar has functioned as the world's dominant reserve currency since World War II. Today, central banks hold about 60% of their foreign exchange reserves in dollars. About half of international trade is invoiced in dollars, and about half of all international loans and global debt securities are denominated in dollars. In foreign exchange markets, where currencies are traded, dollars are involved in nearly 90% of all transactions. The dollar is the preferred currency for investors during major economic crises, as a 'safe haven' currency. During the global financial crisis of 2008-2009, for example, and amidst the economic turmoil associated with the Coronavirus Disease 2019 pandemic in 2020, investors sought U.S. dollars, expecting the dollar to retain its value. In both crises, the U.S. Federal Reserve adopted extraordinary monetary authorities and currency swap lines with other central banks to provide liquidity and dollars."
CRS In Focus, IF11707
Congressional Research Service: https://crsreports.congress.gov/