Why Shielded wire has a grounded conductive braid or foil wrapped around the inner conductor. That shield intercepts electric fields, so stray RF or noise outside the cable cannot induce signals on the center conductor, and signals carried inside the cable cannot radiate out. That is why audio leads, microphone cables, and coaxial feedlines are shielded.
Watch out Reducing receiver overload is tempting because shielding does help keep interference out, but overload is a front-end problem usually fixed with filters or attenuators, not a property of the wire. Shielding does not change the conductor's resistance or its current rating, since those depend on the center conductor's size and material.
Shield = a fence around the wire: keeps signals in, keeps noise out.