In freezing which principle is used?

In freezing crystallization principle is used.
Freezing, also known as solidification, is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point.
Most liquids freeze by crystallization, the formation of a crystalline solid from the uniform liquid. This is a first-order thermodynamic phase transition, which means that as long as solid and liquid coexist, the temperature of the whole system remains very nearly equal to the melting point due to the slow removal of heat when in contact with air, which is a poor heat conductor.
Crystallization consists of two major events, nucleation and crystal growth.