In electrical / studio terms, an unbalanced line consists of just two connections - earth or ground and the signal itself.

Compare balanced line.

A situation in which a mass or system of masses is arranged in such a way that it's center of mass is not uniformly in the center.

ex:: A vehicle with too much wieght on one side is unbalanced, and thus has control issues.

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In the studio, unbalanced cables are indeed a signal and ground. Why this is bad: the cable tends to pick up electromagnetic interference. Whereas an unbalanced line is specially designed to invert one of the signal paths as it flows down the cable. At the end where the cable plugs in, that line is re-inverted, and super-imposed on to the original signal, cancelling out the noise that was added during the run of the cable.

Un*bal"anced (?), a. [In senses 1 and 2, pref. un- not + balanced; in sense 3, 1st pref. un- + balance.]

1.

Not balanced; not in equipoise; having no counterpoise, or having insufficient counterpoise.

Let Earth unbalanced from her orbit fly. Pope.

2. Com.

Not adjusted; not settled; not brought to an equality of debt and credit; as, an unbalanced account; unbalanced books.

3.

Being, or being thrown, out of equilibrium; hence, disordered or deranged in sense; unsteady; unsound; as, an unbalanced mind.

Pope.

 

© Webster 1913.