Analogue audio can either be transferred as an unbalanced or balanced signal, both types in everything from mono to stereo and multichannel audio.
The unbalanced audio cables with either Phono RCA, Jack, or DIN plugs are the most common and used in most amplifiers, players, computers and so on. Common to unbalanced audio cables is that they all consist of one conductor and one ground connection per audio channel per direction.
Balanced signals, typically transmitted with XLR cables, are usually used in professional audio solutions, or in high-end systems, as this transfer type is more immune to noise. Balanced audio cables use 2 conductors for the signal (+/-), as well as one ground connection per channel.