A phase change, also known as a phase transition, is a transformation in the physical state of a certain sample of matter. The phrase is most commonly used to describe the transition of a material between solid, liquid, gaseous and plasma states.
These phase changes are transitions in the thermodynamic states of matter propelled by changes in temperature and pressure. The most easily identified example of a material undergoing phase change is a block of ice melting into water and subsequently evaporating as steam while temperature rises. Different materials have different points of temperature or pressure at which they will undergo a phase change. For water, the point at which the solid form is differentiated from liquid is 32 degrees Fahrenheit.