The four phases of matter are solid, liquid, gas and plasma. Substances can move between these states of matter based on changes in pressure and temperature.
As temperature increases, a solid turns into a liquid by melting, and a liquid turns into gas by vaporization. A gas can turn into plasma through the process of ionization, while the reverse occurs through deionization. In the other direction, a gas becomes a liquid via condensation, which becomes a solid by freezing. In addition to the traditional four phases, some non-classical states of matter include glass, liquid crystal states, quantum spin liquid, superfluids and degenerate matter.