Forex” is the abbreviation most used today for “foreign exchange,” meaning the price of one currency in terms of another currency. By definition, all Forex prices refer to the relationship between two currencies, i.e., a pair of currencies.
The term “Forex” is used interchangeably with the term “FX.” Both are used today and both refer to the same thing, foreign exchange. The term “FX” is mostly used in the US while “Forex” was more broadly used in the UK until recently. Professional traders in the US at banks and brokers tend to use the term “FX” while “Forex” is the term used in the retail market, adopted from the British usage. Also used is the word “currency,” as in “I trade currencies” or “something happened in the currency market.”
Foreign exchange refers literally to money, or more accurately, to money in two different denominations. The “exchange” part of the term means giving one thing of monetary value in return for a different thing of equivalent value. The word exchange refers to the transaction in which each of two parties is willing to exchange his respective basket of money for the equivalent amount of money denominated in the second currency. The price at which the two parties are willing to make the exchange is the exchange rate.
The price of one currency in terms of another currency is called a “rate” and not a “price,” although the word “price” is equally valid and often used. Foreign exchange is the only market in which the word rate is used in place of the word price. The reason for this usage is probably due to the word “rate” being used since the Middle Ages to refer to a tariff or tax levy, since converting one currency to another entails applying a ratio or a proportion to one currency relative to the other. A common Latin phrase is “pro rata” from “pro rata parte,” meaning “in proportion.” The word “rate” in English comes from the Latin.