A flip-flop is a special kind of electronic switch. It's a logic element, and can hold one bit of binary memory (either on or off, 1 or 0,..). Large numbers of these, as in static RAM, allow storing large amounts of information. There are many types of flip-flop Electrical circuits such as D-flip flop, Latch, etc.
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The first electronic flip-flop was invented by William Eccles and F. W. Jordan in 1918. Early flip-flops were called trigger circuits.