A digital logic circuit that can be in one of two states which it switches (or "toggles") between under control of its inputs. It can thus be considered as a one bit memory. Three types of flip-flop are common: the SR flip-flop, the JK flip-flop and the D-type flip-flop (or latch).
Early literature refers to the "Eccles-Jordan circuit" and the "Eccles-Jordan binary counter", using two vacuum tubes as the active (amplifying) elements for each bit of information storage. Later implementations using bipolar transistors could operate at up to 20 million state transitions per second as early as 1963.