Metastability denotes the phenomenon when a system spends an extended time in a configuration other than the system's state of least energy. During a metastable state of finite lifetime all state-describing parameters reach and hold stationary values. While in isolation:

• the state of least energy is the only one the system will inhabit for a definite amount of time, until more external energy is added to the system (unique "absolutely stable" state);
• the system will spontaneously leave any other state (of higher energy) to eventually return (after a sequence of transitions) to the least energetic state.