Forex refers to the foreign exchange market.
It's where all foreign currencies of the world are traded and is one of the most actively traded markets in the world with an average daily trading volume of $5 trillion.
In the forex market, buyers and sellers (individuals, companies, and central banks) trade currency between each other at an agreed price.
If you have ever traveled abroad, then it's likely you have made a forex transaction.
While a lot of buying and selling is done for practical purposes, the majority of forex trading is undertaken with the aim of earning a profit, which can be very profitable with the right strategies.