forex

The foreign exchange market (forex, FX, or currency market) is a worldwide decentralized over-the-counter financial market for the trading of currencies. Financial centers around the world function as anchors of trading between a wide range of different types of buyers and sellers around the clock, with the exception of weekends. The foreign exchange market determines the relative values of different currencies.[1]
The primary purpose of the foreign exchange market is to assist international trade and investment, by allowing businesses to convert one currency to another currency. For example, it permits a US business to import European goods and pay Euros, even though the business's income is in US dollars. It also supports speculation, and facilitates the carry trade, in which investors borrow low-yielding currencies and lend (invest in) high-yielding currencies, and which (it has been claimed) may lead to loss of competitiveness in some countries.[2]
In a typical foreign exchange transaction a party purchases a quantity of one currency by paying a quantity of another currency. The modern foreign exchange market started forming during the 1970s when countries gradually switched to floating exchange rates from the previous exchange rate regime, which remained fixed as per the Bretton Woods system.
The foreign exchange market is unique because of its
huge trading volume, leading to high liquidity
geographical dispersion
continuous operation: 24 hours a day except weekends, i.e. trading from 20:15 GMT on Sunday until 22:00 GMT Friday
the variety of factors that affect exchange rates
the low margins of relative profit compared with other markets of fixed income
the use of leverage to enhance profit margins with respect to account size
As such, it has been referred to as the market closest to the ideal of perfect competition, notwithstanding market manipulation by central banks.[citation needed] According to the Bank for International Settlements,[3] average daily turnover in global foreign exchange markets is estimated at $3.98 trillion, as of April 2007. $3.21 Trillion is accounted for in the world's main financial markets.
The $3.21 trillion break-down is as follows:

$1.005 trillion in spot transactions
$362 billion in outright forwards
$1.714 trillion in foreign exchange swaps
$129 billion estimated gaps in reporting