Phases

A phase is defined a homogeneous form of matter that can be physically distinguished from any other such phase by an identifiable interface. Pedestrian examples are the solid phases, liquid phase, and vapor phase of pure water. Less obvious are the FCC and BCC phases of iron-carbon-nickel-chromium steel or the ferromagnetic and non-ferromagnetic phases of LaSrMnO manganites.

I'll take this opportunity to quote one of my heros:

We may call such bodies as differ in composition or state, different phases of the matter considered, regarding all bodies which differ only in quantity and form as different examples of the same phase.

&dotfill#dotfill;J. W. GIBBS in Trans. Connecticut Acad. III. (1875) page 152