Specific state of Thermodynamic system with all phases staying at Thermodynamic equilibrium.
An important property of Phase Equilibrium is that it honours Gibbs Phase Rule.
See also
Natural Science / Physics / Thermodynamics / Thermodynamic system / Phase
[ State of matter ][ Pure substance ] [ Mixtures ][ Fluid Mixtures ]
[ Thermodynamic equilibrium ][ Vapour Liquid Equilibrium (VLE) ]
[ Phase Equilibrium Diagram ][ Gibbs Phase Rule ]