Could have known and should have known . Click the cross reference. CPI - Consumer Price Index. Notes are paper currency and coins are metal currency. 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.