WordNet (r) 3.0 (2006):

musical instrument digital interface
    n 1: a standard protocol for communication between electronic
         musical instruments and computers [syn: musical instrument
         digital interface, MIDI]

The Free On-line Dictionary of Computing (30 December 2018):

Musical Instrument Digital Interface
MIDI

    (MIDI /mi'-dee/,
   /mee'-dee/) A hardware specification and protocol used to
   communicate note and effect information between synthesisers,
   computers, music keyboards, controllers, and other electronic
   music devices.  It is basically a high-speed serial
   connection with separate connections for MIDI in, MIDI out and
   MIDI through (to allow devices to be chained).

   The basic unit of information is a "note on/off" event which
   includes a note number (pitch) and key velocity (loudness).
   There are many other message types for events such as pitch
   bend, patch changes and synthesizer-specific events for
   loading new patches etc.

   There is a file format for expressing MIDI data which is like
   a dump of data sent over a MIDI port.

   The MIME type "audio/midi" isn't actually registered so it
   should probably be "audio/x-midi".

   Filename extension: .mid or .midi

   (http://update.uu.se/~vick/Coordinator.html).

   Usenet newsgroups: news:comp.music.midi,
   news:alt.music.midi.

   (1998-06-27)