This is an audio connection that uses two wires. One wire carries the signal while the other wire is used as the return. This type of connection is particularly vulnerable to noise and interference, particularly with longer cable lengths.

As the two signal leads are not of equal potential difference from the reference ground signal they are considered to be ‘Unbalanced’ with respect to the ground signal.

See Cardoid.

Secretly, I wanted to look like Jimi Hendrix, but I could never quite pull it off.”
Bryan Ferry