From The Collaborative International Dictionary of English v.0.48:

audio \audio\ n.
   the part of a transmitted signal which conveys the sound of
   the event represented by the signal, such as that of a
   television program. "they always raise the audio for
   commercials"

   Syn: sound.
        [WordNet 1.5]

   2. 1 an audible acoustic wave frequency.

   Syn: audio frequency
        [WordNet 1.5]

   3. the sound elements of television.
      [WordNet 1.5]

From WordNet (r) 2.0:

audio
     n 1: the audible part of a transmitted signal; "they always raise
          the audio for commercials" [syn: sound]
     2: an audible acoustic wave frequency [syn: audio frequency]
     3: the sound elements of television

From The Free On-line Dictionary of Computing (27 SEP 03):

audio
     
        <file format> Sound, one component of multimedia.  Computers
        (and audio compact discs and digital audio tape) work with
        digital audio, in contrast to vinyl disks or analogue tape.
     
        (1999-07-30)