If J and K are both high at the clock edge then the output will toggle from one state to the other. If J and K are both low then no change occurs. The inputs are labeled J and K in honor of the inventor of the device, Jack Kilby. If J and K are different then the output Q takes the value of J at the next clock edge.
It has the input-following character of the clocked D flip-flop but has two inputs,traditionally labeled J and K. The J-K flip-flop is the most versatile of the basic flip-flops.
