The taut, smooth outer layer of dough that you create during shaping by dragging the dough across an unfloured surface.
Surface tension is what keeps your shaped loaf from spreading into a flat disc. By dragging the dough across the counter, you stretch the outer gluten layer taut, creating a "skin" that holds everything together. If the surface tears, you've over-tightened it -- let it rest 10 minutes and try again. Using flour during shaping prevents surface tension from forming, which is why you shape on a clean, unfloured surface and only add flour to the top for banneton placement.
