Forex (‘foreign exchange’ or ‘fx’) describes trading currencies in pairs, like EURUSD, on a decentralised over-the-counter global market. This allows traders to potentially profit from the increased (or decreased) value of a country’s currency in comparison to another. Each currency has an official abbreviation - in this case, EUR means ‘Euro’ & USD means ‘United States Dollar’.
When trading forex online, your base currency is shown first (here as EUR) and is followed by the quote currency (here as USD). The values of these currencies change quickly which is reflected in the spread, i.e. the difference between bid & ask price. You can trade online on the performance of currency pairs by opening a single position on a secure trading platform.