Because phase boundaries relate to changes in the organization of matter, such as a change from liquid to solid or a more subtle change from one crystal structure to another, this latter usage is similar to the use of 'phase' as a synonym for state of matter. Also, the term phase is sometimes used to refer to a set of equilibrium states demarcated in terms of state variables such as pressure and temperature by a phase boundary on a phase diagram. The term phase is sometimes used as a synonym for state of matter, but there can be several immiscible phases of the same state of matter. The glass of the jar is another separate phase. 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. A simple description is that a phase is a region of material that is chemically uniform, physically distinct, and (often) mechanically separable.

: 86 : 3 Examples of physical properties include density, index of refraction, magnetization and chemical composition. In the physical sciences, a phase is a region of space (a thermodynamic system), throughout which all physical properties of a material are essentially uniform.

What is solid matter