The foreign exchange market (Forex, FX, or currency market) is a global decentralized platform for the trading of currency pairs (i.e USD/EUR). This market allows traders to buy and sell global currencies. In terms of volume, it is by far the largest financial market in the world and one of the most volatile.
Currencies are traded as pairs, For example - 1 USD/1 Euro or 1 USD/16 ZAR and prices can change within minutes.