The Free On-line Dictionary of Computing (30 December 2018):
An edge triggeredSR flip-flop with extra logic
such that only one of the R and S inputs is enabled at any
time. This prevents a race condition which can occur when
both inputs of an RS flip-flop are active at the same time.
In a JK flip-flop the R and S inputs are renamed J and K. The
set input (J) is only enabled when the flip-flop is reset and
K when it is set.
If both J and K inputs are held active then the outputs will
change ("togle") on each falling edge of the clock. JK
flip-flops can be used to build a binary counter with a
[Was it named after Jack Kilby?]