Fiat Money

Fiat money is any money whose value is determined by legal means rather than the relative availability of goods and services. Fiat money may be symbolic of a commodity or government promises.

Fiat money provides solutions to several limitations of commodity money. Depending on the laws, there may be little or no need to physically transport the money - an electronic exchange may be sufficient. Its sole use is as a medium of exchange so its supply is not limited by competing alternate uses. It can be printed without limit, so there is no limit on trade volumes.

Fiat money, especially in the form of paper or coins, can be easily damaged or destroyed. However, it has an advantage over commodity money in that the same laws that created the money can also define rules for its replacement in case of damage or destruction. For example, the US government will replace mutilated paper money if at least half of the bill can be reconstructed. By contrast commodity money is gone for good.

Paper money is especially vulnerable to everyday hazards: from fire, water, termites, and simple wear and tear. Money in the form of minted coins is sometimes destroyed by children placing it on railroad tracks or in amusement park machines that restamp it. In order to reduce replacement costs, many countries are converting to plastic bills. For example, Mexico has changed its twenty and fifty pesos notes, Singapore its $2 and $10 bills, Malaysia with $1,$5,$10,$50 and $100, and Australia and New Zealand their $5, $10, $20, $50 and $100 to plastic for the increased durability.

Some of the benefits of fiat money can be a double-edged sword. For example, if the amount of money in active circulation outstrips the available goods and services for sale, the effect can be inflationary. This can easily happen if governments print money without attention to the level of economic activity or if counterfeiters are allowed to flourish.

Perhaps the biggest criticism of paper money relates to the fact that its stability is highly dependent on the stability of the legal system backing the currency. Should the legal system fail, so would the currency that depends on it.

Reference:
Money:Wikipedia.