A scarp of vertical rock is usually known as a cliff, crag, precipice, or wall. But when the terrain in question lies at an angle that’s no steeper than, say, sixty degrees, mountaineers will refer to it as a slab—for example, Satans Slab, a massive, tilted plane of red sandstone among the Flatirons above Boulder, Colorado. If polished by glaciation or water, a slab can be mirror-smooth and very challenging to ascend, in which case it may be called a friction slab.

Jon Krakauer