What is the definition of A Pair?

The word pair is most often used in the forex markets to refer to the pricing of two assets with respect to each other. For example, USD/GDP is a currency pair, as are all currency quotations.

The currency pair shows how much of the first currency (called the base) will buy you of the second (called the quote) currency, i.e. USD/GDP at 0.67 means that PS0.67 will buy $1. Currencies are always quoted in pairs, as you must always exchange one currency for another.