Foie gras is fatty liver, not necessarily foie gras. Most of the market is duck liver, and you will see a big goose liver followed by a small duck. Foie gras is foie gras.

Googse liver=foie d'oie, so I don't want to wait without gras. If you have to translate it into English, it is fatty liver, but it is easier to be understood as hepatomegaly. So it's better not to translate.