Sheathing is the outer plastic or metal insulation material of a cable. Inside the sheathing is insulated wires and sometimes a bare wire (ground wire). The sheathing is what makes a cable a cable. A cable is multiple insulated wires and sometimes a bare wire (ground wire) insulated by the sheathing. A wire is just a single solid conductor or threaded conductor that is insulated. It isn't until you have multiple wires protected by this sheathing, does it become a cable.