Forex or FX, short for FOReign EXchange is the global market where one currency is exchanged for another. To put it simply, when you travel from one country to another and need to change your country currency to that of the country you are travelling to, that exchange is done in the Forex market.
Another major use of the Forex market is when you buy an item from another country; either you or the seller from whom you are buying is using the Forex market to exchange currencies. As evidenced by the above two examples, sometimes without realising it, hundreds of millions of people are using the Forex market every day for convenience purposes. There are also tens of millions who take advantage of the fluctuation created in the Forex market to make a profit.