Around these parts, it usually means camping way off the beaten path, on state or federal land, where there are no regular campsites. It also usually means something different than your usual backpacking trip. Back in the 70s and 80s, I backpacked in quite a few designated wilderness areas but never built a fire. And even in huge wilderness areas, people often camped in the same places along the trail. A lot of these sites became devoid of firewood and the blackened stones from fires littered the area. It's one of the reasons people started carrying backpacking stoves.
The exception was when people did "bushwhacking," i.e., backpacking off the hiking trails on the map. But even then, fires were often used just for comfort. Cooking was almost always done with a backpacking stove.
At any rate, I'm not sure there is any totally agreed upon definition of the term "wild camping."
