Currency pairs are just the two currencies that make up a foreign exchange rate. For example, EUR/USD. There are lots of them so if you see anything written down that way, it is probably a 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.