A surface is called superhydrophobic when water droplets cannot wet it; this means that the droplet, upon coming in contact with the surface, remains spherical (it does not spread) and simply rolls off, carrying along the dust, dirt or debris it that finds in its way, leaving the surface clean.
Superhydrophobic surfaces are comprise of hydrophobic materials (such as wax, oil or fluor containing polymers like Teflon), with ‘rough’ surfaces formed of bumps about 100 nm in height.