FLIP-FLOP is another name of Bi-stable Multi-vibrator. A flip-flop is the basic element of sequential circuit. It has the capability of storing 1 bit. The circuit of the Bi-stable Multi- vibrator using transistors is as follow:
The two transistors are used to store a single bit and they can hold data without external assistance as far as power is supplied to the circuit. If Q is high we get high as an input to the transistor T1 and hence Q bar is low and as Q bar is low we get LOW as input to transistor T2 and hence Q is HIGH. We can see how output is maintained by the circuit itself. So we don’t need t refresh the circuit again and again.