In the physical sciences, a phase is a region of material that is
chemically uniform, physically distinct, and (often) mechanically separable.
In a system consisting of ice and water in a glass jar, the ice cubes are one
phase, the water is a second phase, and the humid air is a third phase over
the ice and water. The glass of the jar is another separate phase. (See state
of matter § Glass.)
More precisely, a phase is a region of space (a thermodynamic system),
throughout which all physical properties of a material are essentially
uniform.: 86 : 3 Examples of physical properties include density, index of
refraction, magnetization and chemical composition.