nothing in this world is such as digital everything is analog.we consider it as digital.
like the clock waveform which we use in digital systems is actually an analog clock.
i think people with diferent views put in different ways.
Metastability is a state where your flip flop output is neither in a 1 or 0 state. It is in a transitioning state and could go into 1 or 0, depending on the flop characteristics. This uncertainty can be due to a violation in the flops setup or hold time.
When ever there is setup and hold time violations in any flip-flop, Flip-flop enters a state, where its output is unpredictable, this state is know as metastable state (quasi stable state), at the end of metastable state, Flip-Flop settles down to either '1' or '0'. This whole prcoess is know as metastability