Gate
Gate (Trigger) also has two implementations:
V-Trigger ("voltage trigger", sometimes called "positive trigger"). This method involves keeping normally low voltage (around 0V) on trigger and producing a fixed positive voltage to indicate a note is on. The amount of voltage required differs from synth to synth, but generally it is from 2 to 10 V. V-Trigger is used by Roland and Sequential Circuits synths, among others.
S-Trigger ("short circuit trigger", sometimes called "negative trigger"). This one involves keeping voltage high normally, shorting the trigger circuit whenever the note should play. S-Trigger is used by Moog, Korg and Yamaha synths, among others.