structural:scholar_edition
Locality

The definition of money says it is money only "in a particular country or socio-economic context". In general, communities only use a single measure of value, which can be identified in the prices of goods listed for sale. There might be multiple media of exchange, which can be observed by what is given to purchase goods ("medium of exchange"), etc. In most countries, the government acts to encourage a particular forms of money, such as requiring it for taxes and punishing fraud.

Some places do maintain two or more currencies, particularly in border towns or high-travel areas. Shops in these locations might list prices and accept payment in multiple currencies. Otherwise, foreign currency is treated as a financial asset in the local market. Foreign currency is commonly bought or sold on foreign exchange markets by travelers and traders.

Communities can change the money they use, which is known as currency substitution. This can happen intentionally, when a government issues a new currency. For example, when Brazil moved from the Brazilian cruzeiro to the Brazilian real. It can also happen spontaneously, when the people refuse to accept a currency experiencing hyperinflation (even if its use is encouraged by the government).

The money used by a community can change on a smaller scale. This can come through innovation, such as the adoption of cheques (checks). Gresham's law says that "bad money drives out good". That is, when buying a good, a person is more likely to pass on less-desirable items that qualify as "money" and hold on to more valuable ones. For example, coins with less silver in them (but which are still valid coins) are more likely to circulate in the community. This may effectively change the money used by a community.

The money used by a community does not have to be a currency issued by a government. A famous example of community adopting a new form of money is prisoners-of-war using cigarettes to trade.