Glossary of Terms:
 
controller
1) In MIDI, a device that generates a MIDI signal to control synthesizers, sound modules or sample playback units.
2) A remote control unit for a multitrack tape machine which controls transport functions as well as monitor selection switching functions and record ready/safe status of each track.
3) Any device generating a control voltage or signal fed to the control input of another device.
4) A control change number generated by a MIDI device to control a specific MIDI function.
Source: Recording Institute of Detroit

Also refered as:
  MIDI controller
Related terms:
  MIDI   program change   sequencer