reset/set flipflop
The designation RS flip-flop is directly related to the designation of the inputs: "R" stands for Reset, "S" for Set.
Such a RS flipflop has two outputs "Z" and "Z*" (Z inverse). Depending on the last state of the flipflop, a change of state at one input results in a change at the outputs. The RS flipflop knows an undefined state if both inputs are set to "1".