Glossary of Terms
 
  trigger  
  1) The signal or the action of sending a signal to control the start of an event.
2) The control of a dynamics processing device by an external audio signal.
3) A device, which puts out a signal to control the start of an event, including a device that puts out such a signal when struck.
 
  Source: Recording Institute of Detroit  

Also refered as:
  key