In French, I read a couple of times this expression, what does it mean? “formules à volonté”?
It is basically a meal plan where you can reorder as much as you care. It is not exactly the typical "all-you-can-eat" as a "formule" is not necessarily a buffet. In France, some restaurants will offer this for instance with meals such as a "fondue bourguignonne", a "raclette" or mussels.