Source : Webster's Revised Unabridged Dictionary (1913)

Microphone \Mi"cro*phone\, n. [Micro- + Gr. ? sound, voice: cf.
   F. microphone.] (Physics)
   An instrument for intensifying and making audible very feeble
   sounds. It produces its effects by the changes of intensity
   in an electric current, occasioned by the variations in the
   contact resistance of conducting bodies, especially of
   imperfect conductors, under the action of acoustic
   vibrations.

Source : WordNet®

microphone
     n : device for converting sound waves into electrical energy
         [syn: {mike}]

Source : Free On-Line Dictionary of Computing

microphone
     
         Any electromechanical device designed to
        convert sound into an electrical signal.
     
        A microphone converts an acoustic waveform consisting of
        alternating high and low air pressure travelling through the
        air into a voltage.  To do this it uses some kind of pressure
        or movement sensor.  The simplest kind of microphone is
        actually very similar in construction to a {loudspeaker}.
     
        The analogue electrical signal can be fed into a computer's
        {sound card} where it is amplified and {sampled} to convert it
        into a {digital} waveform for storage or transmission.
     
        (2002-11-04)