Currency and exchange were important elements of trade in the ancient world, enabling people to buy and sell items like food, pottery, and raw materials. If a Greek coin held more gold than an Egyptian coin due to its size or content, then a merchant could barter fewer Greek gold coins for more Egyptian ones, or for more material goods. This is why, at some point in their history, most world currencies in circulation today had a value fixed to a specific quantity of a recognized standard like silver and gold.
Forex is a portmanteau of foreign currency and exchange. Foreign exchange is the process of changing one currency into another currency for a variety of reasons, usually for commerce, trading, or tourism. According to a recent triennial report from the Bank for International Settlements (a global bank for national central banks), the average was more than $5.1 trillion in daily forex trading volume.