Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process.
An example is a state of matter change, meaning a phase transition, such as ice melting or water boiling.
The term was introduced around 1762 by Scottish chemist Joseph Black. It is derived from the Latin latere (to lie hidden). Black used the term in the context of calorimetry where a heat transfer caused a volume change while the thermodynamic system's temperature was constant.