Currency pair it is a term used for determination of cross currency rates for certain pair of currency in Forex trading market.

There are 4 mayor currency pairs  - Euro against US dollar, US dollar / Japanese yen, British pound / US dollar, and US dollar / Swiss franc ( EUR/USD, USD/JPY, GBP/USD, and USD/CHF respectively).

First currency in the pair called “base currency” and the second - “quote qurrency“. The value of the currency pair shows how much of the “quoted currency” needed for purchasing single unit of “base currency“.

All currencies on foreign currency exchange market are traded simultaniosly and each currency pair could be counted as a single unit itself. You can buy currency pair or sell it, like goods or shares ont other market exchanges. If you buy certain currency pair it means you are buying “base currency” in this pair and selling “quote currency“.