Music Instrument Digital Interface

MIDI (/ˈmɪdi/; short for Musical Instrument 'Digital' Interface) is a technical standard that describes a , digital interface, and electrical connectors that connect a wide variety of electronic musical instruments, computers, and related music and audio devices. A single MIDI link can carry up to sixteen channels of information, each of which can be routed to a separate device.

MIDI carries event messages that specify notation, pitch and velocity (loudness or softness), control signals for parameters such as volume, vibrato, audio panning from left to right, cues in theatre, and clock signals that set and synchronize tempo between multiple devices. These messages transmit via a MIDI cable to other devices, where they control sound generation and other features. In a simple example of a MIDI setup, a MIDI keyboard or other controller triggers a sound module to generate sound, which a keyboard amplifier or other amplification makes audible. MIDI data can also be recorded into a hardware or software device called a sequencer, where a musician can edit the data and play it back later.

A file format that stores and exchanges the data is also defined. Advantages of MIDI include small file size, ease of modification and manipulation and a wide choice of electronic instruments and synthesizer or digitally-sampled sounds. Prior to the development of MIDI, electronic musical instruments from different manufacturers could generally not communicate with each other. With MIDI, any MIDI-compatible keyboard (or other controller device) can be connected to any other MIDI-compatible sequencer, sound module, drum machine, synthesizer, or computer, even if they are made by different manufacturers.

...
Wikipedia