What is turning a liquid into a solid called?

Freezing is the term used to describe the formation of a solid from a liquid.

Freezing is one example of a phase change. During a phase change, one state of matter is changed into another. All phase changes are physical changes because the composition of a substance does not change during phase changes. For example, water has a molecular formula of H2O whether it is a liquid, solid, or a gas.

Phase changes are a result of a change in the kinetic energy obtained by the particles of a substance. Kinetic energy is the energy of motion. As particles lose kinetic energy, they slow down, come closer to one another, and take on a more definite shape and volume. Freezing, condensation, and deposition are phase changes that result from a loss in kinetic energy. As particles gain kinetic energy, they begin to move faster, move apart from one another, and take on a more indefinite shape and volume. Melting, evaporation, and sublimation are phase changes that result from an increase in kinetic energy.