Metastable State :

The excited state of an atom tomorrow molecule having a relatively long lifetime is called metastable state.
The excited electrons can move from E1 to E2 around the nucleus of an atom, then when they return back to their normal state which is ground state electrons will emit the protons in order to lose the energy.
It is a special type of excited state where the lifetime of an atom is more than the normal excited state.
Metastable state plays an important role in lacing action.
In metastable state atoms stay in the order of 10^-3 to 10^-2 second.

Metastable State In Laser