Paper Money: US
Numismatics or coin collecting/paper money collecting is the study, collecting and/or trading of coins and currency notes or other forms of legally minted or printed documents of payment used to resolve debts and the exchange of goods. Frequently collected coins and paper money include those that were in circulation for only a brief time, minted or printed with errors or especially beautiful/historically interesting!
Money as such, even before the coming of the minted coins or the printed notes, must have been a thing of either inherent or perceived value. What all has not been used as money since the times immemorial! Precious metals, conch shells, cigarettes, horses and even the goatskin have all been things of such value. Modern money (or even old money for that matter, having a collector's value in addition as well!) has simply been assigned a status to be perceived as having a value in it.
I-Ching Coin
