Metastable state
From Soft-Matter
Introduction
A metastable state is a state of a system which is stable over one time-scale and unstable over another timescale. It represents a local, but not global, minimum in the energy landscape of the system. In chemistry, a reaction may not take place quickly if the reactants are stuck in a metastable state intermediate between the initial reactants and desired products. In order to progress to the final desired products, the reactants must overcome the activation energy of the reaction to transfer from the metastable state to the stable state.

Depiction of metastable state where state 1 is the metastable state, state 2 is the transition state, and state 3 is the stable state. (Image from Wikipedia)