Foreign exchange trading is the buying or selling of one currency in relation to another. Since all currencies are priced differently, this price difference can result in profit as the values of the currencies change.
The FX market is estimated to have a turnover value of over $5 trillion a day.
This is the result of individuals, companies, banks, funds, and governments buying and selling global currencies all day every day until Friday close at 1700 ET and reopens Sunday 1700 ET.
This turnover can be the result of import/export activities, hedging against currency risk, or speculating on the change of currency values.
Since you can normally exchange currencies through an exchange office or bank, this type of trading is not centralized in a major national exchange like stocks or futures.
This setup makes it extremely flexible, customisable and accessible.