In electronics, a trigger is something used to initiate some action. In circuits this is often some form of electrical pulse. For example, an electronic drum set may respond to pulses generated by striking a surface with some type of transducer attached to it. On the other hand a slightly looser definition would include the triggering of a sound in a keyboard or sound module from another keyboard. In this case it may be much more than a pulse that is transmitted. With MIDI a whole series of data is required to “trigger” the sounding of one note.