What is MIDI and General MIDI?

MIDI is Musical Instrument Digital Interface, which is a language by which keyboards, other MIDI instruments, and computers can universally communicate. When a note is played on a keyboard, the computer registers what note was played, how long it was held, and the tone number of the instrument. Then, when it connects to another keyboard and played back it will play the same.

General MIDI was developed because Casio, Roland, Yamaha, and other manufacturers would all have their own numbering system. Someone could use a Casio piano tone to record a song, but when the song was played back on a Yamaha, it would produce a guitar sound. General MIDI took 128 specific tones and assigned them to the same numbers, so that a composition plays the same on any General MIDI instrument no matter what the manufacturer.