MIDI 
Musical Instrument Digital Interface 
A hardware protocol (pronounced "middy") that enables communication between computers and synthesizers, keyboards, and sound cards used in composing and recording digital music. With a computer running MIDI-compatible software, you can record sounds produced by connected instruments and manipulate the sounds however you wish. MIDI files contain instructions for producing sound (note and effect information, pitch, dynamics, decay rate, and stereo position) rather than actual digitized music and thus are much smaller than sound files. Because MIDI files create no sound on their own, they must be played back by a synthesizer, a drum machine, or a virtual instrument.