1º_ Lexical component by hearing, in the sense of perceiving sound waves. From the Latin audio, is, ire ("to hear, to hear"). 2º_ It is used as a noun for what is audible, what is for hearing, especially for sound recordings.
It is the electrical or magnetic tension proportional to a sound, it is generated by elements transducers * as they are microphones and it is usually accompanied by various steps and processes for their processing, storage and reproduction.