MIDI ( /ˈmɪdi/; short for Musical Instrument Digital Interface) is an electronic musical instrument industry specification that enables a wide variety of digital musical instruments, computers and other related devices to connect and communicate with one another. It is a set of standard commands that allows electronic musical instruments, performance controllers, computers and related devices to communicate, as well as a hardware standard that guarantees compatibility between them. MIDI equipment captures note events and adjustments to controls such as knobs and buttons, encodes them as digital messages, and sends these messages to other devices where they control sound generation and other features. This data can be recorded into a hardware or software device called a sequencer, which can be used to edit the data and to play it back at a later time. MIDI carries note event messages that specify notation, pitch and velocity, control signals for parameters such as volume, vibrato, audio panning and cues, and clock signals that set and synchronize tempo between multiple devices. A single MIDI link can carry up to sixteen channels of information, each of which can be routed to a separate device. The 1983 introduction of the MIDI protocol revolutionized the music industry.

MIDI technology was standardized by a panel of music industry representatives, and is maintained by the MIDI Manufacturers Association (MMA). All official MIDI standards are jointly developed and published by the MMA in Los Angeles, California, USA, and for Japan, the MIDI Committee of the Association of Musical Electronics Industry (AMEI) in Tokyo.

Read more about MIDI:  Technical Specifications, Extensions, Alternative Hardware Transports, The Future of MIDI