Layers and layers and layers of it, in some areas.
The room I refinished is painted. One wall I pulled down had at least five layers of wallpaper on it. Other parts of the house have comparable amounts of the stuff. Some walls look like they only have a single coat of plain paper that's painted. It's curious to peel away wallpaper to see what the different layers look like although frankly most of them are pretty grim - it's easy to see why someone covered it over but much less easy to figure why anyone would have chosen it in the first place. But the many layers cover 100+ years, so I guess tastes change.
