Raw meat and eggs will be delivered to your plate if you order Tartar. It’s a rather innocuous word, kind of funny and inviting. Vegetarians however should avoid this menu item.
Steak tartar is a common menu item in bistros. It can be served two ways, prepared and unprepared. Those who like to play with their food will get the unprepared version. Raw diced beef will be delivered with an assortment of herbs and a raw egg. It’s their job to mush it all together.
Tuna Tartar is becoming fashionable in the raw-beef aware restaurants of America. You won’t see that often in Paris, just the formerly happy cow variety.
Similar words that can cause confusion are tarter (the sauce normally used on fish) and tartine (a slice of bread with butter or sometimes melted cheese and other goodies).