A form of payment that has been approved by the government as legal tender and is usually accompanied by such legislation. The word "fiat" is derived from Latin and is used to refer to a law, rule, or decision made by the government. Fiat money is by definition money that has no intrinsic value because it is not backed by a physical good and is typically constructed of inert or cheap materials (such as a little sheet of paper). Fiat money is still commonly used as a form of payment. The primary reason fiat money is seen as legitimate and valuable in our culture, aside from official sanction and regulation, is because of a shared belief. To put it another way, the fiat value is heavily reliant on a consensus that it has a market value, can be used as a medium of exchange, and has an inherent purchasing power. Fiat money is so heavily reliant on social convention (and the belief that it will retain its worth in the future) as well as a government decision. The real worth of the currency, as a means of exchange, is swiftly and significantly diminished if either the societal belief or the governmental mandate is challenged. Since the majority of fiat currencies are not backed by precious metals (such as gold, silver, and copper) or any other types of commodities, central banks have the power to significantly alter the money supply, which could potentially result in periods of extremely high inflation rates (hyperinflation). According to historical evidence, China's earliest paper currency dates back to the 11th century. The so-called jiaozi, regarded as the first paper currency ever issued by a government, was a specialty of the Song dynasty. Jiaozi was a crude type of banknote designed to take the place of the time's hefty iron money coins. The Great Yuan dynasty that followed, however, was the first to genuinely accept and use fiat money on a massive scale - as the main means of exchange. The Great Yuan dynasty ruled from 1271 until 1368, although the following Great Ming dynasty (1368–1644) continued to use fiat money.