Metastability denotes the phenomenon when an isolated 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:A single particle analogy may be drawn with a ball resting in a hollow on a slope. With some perturbation the ball may start rolling again to lower levels. Isomerisation is another common example, where higher energy isomers are long lived as they are prevented from rearranging to the ground state by (possibly large) barriers in the potential energy.The metastability concept originates in the physics of first-order phase transitions later to acquire new meanings in the study of aggregated subatomic particles (in atomic nuclei or in atoms) or in molecules, macromolecules or clusters of atoms and molecules. Later on it was borrowed for the study of decision-making and information transmitting systems.Many complex natural and man-made systems can demonstrate metastability.