Which term refers to a substance's transitional state from liquid to gas?

The term that refers to a substance's transitional state from liquid to gas is vaporization. This process occurs when the molecules of a liquid gain enough energy to overcome their intermolecular forces and enter the gas phase. Vaporization encompasses both evaporation and boiling; evaporation occurs at the surface of the liquid and can happen at any temperature, while boiling happens throughout the liquid at a specific boiling point.

In the context of the other options, condensation describes the reverse process where gas transforms back into a liquid, precipitation refers to the formation of solid or liquid particles from a solution, typically in the context of meteorological phenomena, and evaporation specifically highlights the process when it occurs at temperatures below boiling. Thus, vaporization is the correct term for the transition from liquid to gas.