MIDI, or Musical Instrument Digital Interface, was developed by Dave Smith (founder of Sequential Circuits and Dave Smith Instruments, with the latter being renamed simply Sequential) and Ikutaro Kakehashi (founder of Roland Corporation and others) and became part of the world of electronic music in 1983.  Think of MIDI as a hotline between MIDI-capable instruments, effects, and other musical devices, with cables carrying the digital signal and MIDI itself being the language or content.