The heat required to convert a substance from liquid to gas without any change in temperature is known as the latent heat of vaporization. This energy is absorbed by the substance during the phase transition from liquid to gas at its boiling point. At this point, the substance absorbs energy to overcome intermolecular forces holding the liquid molecules together, allowing them to enter the gas phase.

The latent heat of vaporization is a critical concept in understanding processes such as boiling, where liquid turns into vapor. It is essential in various applications, including cooking, distillation, and climate science. Different substances have different latent heats of vaporization, depending on their molecular properties and intermolecular forces.

Therefore, the correct answer is [D] Vaporization, as it specifically refers to the phase transition from liquid to gas, accompanied by the absorption of heat energy without a change in temperature.