They are paper and coin currency. Coins are currency. Paper bills are more properly called notes today. Postal money orders and cashier's checks might be included. Silver certificates were long ago called in by the Fed on the day that Vice President Johnson took over after President Kennedy was assassinated.
Currency is an icon or symbol of money.
When created in this manner, we owe no one even one dime for it. It is the opposite of debt money , where money is created by private bankers and loaned to us for interest that is now the national debt. Our Constitution does not direct Congress to create that debt. It eventually destroys the kingdom using it. Our Federal Reseve System is an example.