NEXT (SoC Example: Helium 210)
A pencil balancing on a razor blade can be metastable, but normally flops to one side or the other.
A bistable is two inverters connected in a ring. This has two stable states, but there is also a metastable state.
If a D-type is clocked while its input is changing, it might be set close to its metastable state and then drift to one
level or the other. Sometimes, it will take a fair fraction of a clock period to settle.
The oscillogram shows metastable waveforms at the output of a D-type when set/hold times are sometimes violated.