Real Dictionary

microphone
countable noun: A microphone is a device that is used to make sounds louder or to record them.

microphone in American English
an instrument containing a transducer that converts the mechanical energy of sound waves into an electric signal, used in telephony, radio, sound amplification, etc.
noun: an instrument capable of transforming sound waves into changes in electric currents or voltage, used in recording or transmitting sound

microphone in British English
noun: a device used in sound-reproduction systems for converting sound into electrical energy, usually by means of a ribbon or diaphragm set into motion by the sound waves. The vibrations are converted into the equivalent audio-frequency electric currents

microphone in Electrical Engineering
noun: A microphone is an electromechanical transducer that converts sound pressure into an electrical signal.