The word grenouille (pronounced "gruh-noo-EE") is the French word for frog, and in the culinary arts, the term grenouilles (or cuisses de grenouilles) refers to frog legs as a food.
Frog legs are one of two French foods that, if you remember back to your childhood, the mere mention of which would invariably cause everyone to break into borderline hysterical giggles of disbelief (the other being, of course, snails).
Unless you happen to be French or from the South, since for many kids growing up in either of those places, the idea of frog legs is undoubtedly somewhat less exotic.
And it so happens that frog legs are really good. You might hear that they taste like chicken, but that's not entirely true. Their texture is very much like chicken. And the breading (if they're prepared with breading, which is fairly common) tastes like breading. Furthermore, the seasonings and flavorings all taste like whatever they taste like, and many times you've tasted all of those things in conjunction with chicken.
But frogs taste like frogs—which is to say, slightly swampy and fishy. Like if chicken came from a pond. It's hard to describe, but hopefully you're curious enough that when you have the chance, you'll try them.
Why The Legs and Nothing Else?
The legs are the only edible part of the frog, but they can be quite meaty. They need to be skinned and then soaked in cold water, saltwater, or milk before being cooked. The soaking step is somewhat controversial, owing to the fact that there seems to be no clear reason why it's done, only that it's the way it's always been done (although some cooks suggest that soaking helps reduce the gamy flavor of the frogs).
In any event, the skin is fairly loose and easy to get off. I say this not because you're likely to ever do this on your own, but it's true. And while the skin is edible, it's tough and slimy and, well, froggy. Not to say that one should shy away from the reality of whatever one is eating, but it's also quite tough. You need to snip off the feet as well.
One classic French preparation of frog legs, called cuisses de grenouilles à la Provençale, involves dredging the frog legs in seasoned flour and then sautéeing them in butter or olive oil with garlic and chopped parsley. Another technique is to first blanch the frog legs and then bread them and deep fry them.
Another preparation, which is somewhat more complicated, involves simmering the frog legs in white wine along with butter, lemon, and mushrooms. When the frog legs are cooked, they and the mushrooms are removed and set aside while the sauce is reduced and then thickened with a liaison—a blend of egg yolks and cream.
Finally, when the sauce is thickened, the frog legs and the mushrooms are returned to the sauce and warmed until heated through and then finished with butter, lemon, and fresh chopped parsley. This preparation is known as cuisses de grenouilles à la poulette.