Definition of 'Currency Pair'
The quotation and pricing structure of the currencies traded in the forex market: the value of a currency is determined by its comparison to another currency. The first currency of a currency pair is called the "base currency", and the second currency is called the "quote currency". The currency pair shows how much of the quote currency is needed to purchase one unit of the base currency.
Investopedia explains 'Currency Pair'
All forex trades involve the simultaneous buying of one currency and selling of another, but the currency pair itself can be thought of as a single unit, an instrument that is bought or sold. If you buy a currency pair, you buy the base currency and sell the quote currency. The bid (buy price) represents how much of the quote currency is needed for you to get one unit of the base currency. Conversely, when you sell the currency pair, you sell the base currency and receive the quote currency. The ask (sell price) for the currency pair represents how much you will get in the quote currency for selling one unit of base currency.
For example, if the USD/EUR currency pair is quoted as being USD/EUR = 1.5 and you purchase the pair, this means that for every 1.5 euros that you sell, you purchase (receive) US$1. If you sold the currency pair, you would receive 1.5 euros for every US$1 you sell. The inverse of the currency quote is EUR/USD, and the corresponding price would be EUR/USD = 0.667, meaning that US$0.667 would buy 1 euro.