Metastable is a term used to refer to a close degree to normal stability ranges or values for any given measurable property of a material, varying slightly to a more unstable level due to the absence of certain chemical, physical or energy conditions.
Metastability can be used to describe pitting corrosion. Metastable pits are covered during growth and display a constant current density. Rupture of a pit cover during metastable growth can lead to repassivation of the pit.
Metastable materials or metals can appear to be stable but are capable of attaining a more stable state if given more precise supporting conditions to meet neutrality.