An exchange rate between two currencies is the price of a country's currency in relation to another currency (called a currency pair). An exchange rate thus has two components: the domestic currency and a foreign currency.
Currencies can be quoted either directly (how much 1 domestic currency unit, for example: $1USD is X amount of Euros, is worth in the foreign currency) or indirectly (how much 1 foreign currency unit, for example: 1 Euro is X amount of USD, is worth in the domestic currency).