The constant value is called the residual entropy of the system. If the system does not have a well-defined order (if its order is glassy, for example), then there may remain some finite entropy as the system is brought to very low temperatures, either because the system becomes locked into a configuration with non-minimal energy or because the minimum energy state is non-unique. In such a case, the entropy at absolute zero will be exactly zero. Entropy is related to the number of accessible microstates, and there is typically one unique state (called the ground state) with minimum energy. At absolute zero (zero kelvins) the system must be in a state with the minimum possible energy.

This constant value cannot depend on any other parameters characterizing the closed system, such as pressure or applied magnetic field. The entropy of a system approaches a constant value when its temperature approaches absolute zero. The third law of thermodynamics states, regarding the properties of closed systems in thermodynamic equilibrium:

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