A microphone or 'mic' (pronounced "mike") as it is commonly referred to is a transducer that interfaces between a sound source and an amplification or broadcast process. Effectively it converts an acoustic signal into an electrical signal and by doing so allows the original source to be transferred to an alternative media such as disk, tape or an audio signal for broadcast purposes.
There are many different types of microphone that range from high quality multi-purpose models to specialised categories that are only used for specific purposes. Vocal Microphones in a recording studio are an example of this as they have been specifically designed to capture the dynamic range and natural tone of the human voice.
Different microphones have different patterns of directionality commonly called Polar patterns. This is the immediate area of audio sensitivity around the microphone. The sensitivity is an indication of how efficiently the mic is able to convert acoustic pressure to output voltage.