Global currencies generally fall into two historical categories based on what gives them their baseline market value.
Commodity backing means the paper note represents a specific physical asset stored safely away, such as gold bars or silver bullion. Under this system, cash could be directly redeemed for the hard metal standard.
Today, almost all global tender is fiat money. It holds no underlying material asset value; instead, it is trusted because issuing governments declare it legal tender for settling financial debts.