The process by which a solid becomes a liquid is called melting. Melting is one of the six phase transitions by which matter undergoes a change in state.
Other phase transitions include sublimation, in which a solid is changed into a gas, and deposition, the process in which gas is changed into a solid. The process that changes a liquid into a solid is called freezing. Condensation is the process that takes place in order for a gas to become a liquid, while vaporization occurs when a liquid is transformed into a gas. The concept of phase transitions is used in the field of material study.