Is there a difference between a foreign transaction fee and a currency conversion fee?

A foreign transaction fee is charged when you buy something while traveling abroad (or from a merchant based overseas), while the currency conversion fee is a surcharge from an overseas merchant to convert transactions into dollars. In other words, the currency conversion fee inflates the currency exchange rate. 

Most cards charge a foreign transaction fee of 3%, but there are some cards without foreign transaction fees, like the Capital One Venture. 

The merchant is required to ask you before using currency conversion, which usually adds another 3-10% to your transaction. If you decline, your credit card payment network will do the conversion. The exchange rate via the card network is always better.

To avoid both, get a credit card with no foreign transaction fees and decline the currency conversion.