A balanced transmission line:

A balanced transmission line consists of two parallel, identical wires, such as twin-lead, ladder line, or window line. In a properly functioning balanced line, both wires carry equal but opposite RF currents, and neither wire is connected to ground. This differs entirely from an unbalanced line like coaxial cable, which has one conductor placed inside the other and uses the outer shield as a ground reference. Therefore, options describing a conductor inside another or a single-wire system describe unbalanced or alternative feed methods.