For rigid surfaces immersed in a flow, the no-slip condition on the wall holds. In simplistic terms, the basic idea of our slip wall is to release the no-slip condition to reduce drag. This is achieved with a belt that replaces the rigid wall. The moving belt, driven by the flow shear stress itself, reduces the velocity difference between mean flow and the wall, and thus it reduces the skin friction. Our device should not be confused with an actively driven belt surface like the one of a moving floor in a wind tunnel. We deal with a purely passive device