Minecraft wiki entry for Memory, associated text: A JK flip-flop is another memory element which, like the D flip-flop, will only change its output state when triggered by a clock signal C. They can be edge-triggered (designs A, D, E) or level-triggered (C). Either way, the two inputs are called J and K. These names are arbitrary, and somewhat interchangeable: if a Q̅ output is available, swapping J and K will also swap Q and Q̅.