The foreign exchange market – also called forex, FX, or currency market – was one of the original financial markets formed to bring structure to the burgeoning global economy. In terms of trading volume it is, by far, the largest financial market in the world. Aside from providing a venue for the buying, selling, exchanging and speculation of currencies, the forex market also enables currency conversion for international trade settlements and investments. According to the Bank for International Settlements (BIS), which is owned by central banks, trading in foreign exchange markets averaged $5.1 trillion per day in April 2016.
The main participants in this market are the larger international banks. Financial centers around the world function as anchors of trading between a wide range of multiple types of buyers and sellers around the clock, with the exception of weekends. Since currencies are always traded in pairs, the foreign exchange market does not set a currency's absolute value but rather determines its relative value by setting the market price of one currency if paid for with another. Ex: US$1 is worth X CAD, or CHF, or JPY, etc.
The foreign exchange market is where currencies are traded. Currencies are important to most people around the world, whether they realize it or not, because currencies need to be exchanged in order to conduct foreign trade and business. If you are living in the U.S. and want to buy cheese from France, either you or the company that you buy the cheese from has to pay the French for the cheese in euros (EUR). This means that the U.S. importer would have to exchange the equivalent value of U.S. dollars (USD) into euros. The same goes for traveling. A French tourist in Egypt can't pay in euros to see the pyramids because it's not the locally accepted currency. As such, the tourist has to exchange the euros for the local currency, in this case the Egyptian pound, at the current exchange rate.