A source currency or the base or primary currency is the currency denomination exchanged to obtain the currency of some other country or region. For instance, if you have some money saved up in U.S. dollars, $100, and you want to convert it into Indian Rupees (INR) because you are going on a trip there, you will need to know the foreign exchange rate or what 100 USD equals to INR. Therefore, the U.S. dollars you have in hand are the "source currency" or the currency that needs to be exchanged.

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