MIDI MASTER CONTROLLER
MIDI, is the acronym for Musical Instrument Digital Interface. It is a protocol or digital language, originally invented to provide a means for musical keyboards to communicate, control or sync with each other. MIDI controlled sound synthesizers, lighting systems, and media players, are popular among musicians, composers, and engineers today.
Machines whose only output is MIDI data are becoming increasingly common, and are known as MIDI controllers. Using a master MIDI controller device, one can play or trigger sounds, events, samples, and manipulate electronic functions of other electronic devices, including synthesizers and computers, remotely.
For more information see: Wikipedia's entry on MIDI Controllers