Electrical signal, in particular audio is sent via an alternating current accross a hot wire and a ground wire. This signal is said to be unbalanced.
Unbalanced audio signals are typically encountered in the consumer environment on equipment such as home Hi-Fi, car stereos and computer audio systems. At best, they work well allowing an audio signal to pass from one piece of equipment to the next with minimal interference encountered. At worst they can be pick up undesirable noise and hum and can also cause damage if phantom power is enabled (namely a short circuit) and are usually avoided in professional situations. However unbalanced systems are cheap to manufacturer and make system design less complex when compared to a Balanced system.
Electronic transducers such as instruments and microphones by default have unbalanced outputs, however many professional microphones include transformers to 'balance' the signal while electro-pickup instruments require inpedance conversion using a direct-input(DI)-box to standard line or microphone levels before being balanced and sent to their destination.
Unbalanced audio is often used within balanced devices audio buses, with balancing circuitry only at the input and output sides of the equipment.
A typical unbalanced audio cable may consist of the signal cable (typically carried on the inner core) and a shield. TS Jacks or RCA (phono) cables are associated with unbalanced connections although any electrical connector with two or more pins can carry unbalanced audio (in some cases the ground may be used as a connection so only one additional conductor is required).
Image of an unbalanced cable
Depending on the quality of the cable, shielding consisting of foil may be used to reject audible interference. Audio cable of different qualites is available and in particular, consumers are being offered relatively expensive audio cable of which its advertised benefits are seldom easy to prove.