What does the term 'latent heat' refer to?

Latent heat refers specifically to the heat energy that is absorbed or released during a phase change of a substance, such as melting, freezing, boiling, or condensing, without a change in temperature. This unique property is crucial in understanding thermodynamic processes because it illustrates how energy is used in changing the state of a material, rather than raising its temperature.

For instance, when a solid melts into a liquid, it requires energy (latent heat of fusion) to break the intermolecular bonds without affecting the temperature of the substance. Similarly, when a liquid vaporizes into a gas, it absorbs heat (latent heat of vaporization) without changing its temperature until the entire phase transition is complete. This concept is fundamental in various engineering applications, including refrigeration, heating systems, and understanding weather patterns, where the energy involved in phase changes plays a vital role in system efficiency and function.

The other options focus on different aspects of heat transfer and thermodynamics, which do not encompass the definition of latent heat as accurately as the correct choice does.