A monostable multivibrator
has one stable state and one unstable state, and remains in the stable state until it is triggered by a change in the input state. Once triggered, it is placed in its unstable state and after a time delay staps back to its original condition.
Monostables are used for pulse generators and time-delay generators, frequency
dividers, missing pulse detectors, and for detecting the leading and trailing edges of waveform