The forex (foreign currency exchange) market is the largest and most liquid financial market in the world. The forex market unlike stock markets is an over-the-counter market with no central exchange and clearing house where orders are matched.
Traditionally forex trading has not been popular with retail traders/investors (traders takes shorter term positions than investors) because forex market was only opened to Hedge Funds and was not accessible to retail traders like us. Only in recent years that forex trading is opened to retail traders. Comparatively stock trading has been around for much longer for retail investors.
Recent advancement in computer and trading technologies has enabled low commission and easy access to retail traders to trade stock or foreign currency exchange from almost anywhere in the world with internet access.