Analog audio

The term Analog audio is typically used in contrast to digital audio. Strictly speaking; audio is used to describe things having to do with sound.

Sound is short-term variations in air pressure above an below average (barametric) air pressure. These pressure variations are translated by a transducer such as a microphone into voltage variations for transmission or reproduction via another transducer (speaker) after amplification. The voltage variations change proportionally to the air pressure variations, so one can say the voltage variations are analogous to the sound- or that the voltage waveform is an "analog' of the audio waveform.