What term describes the outflow of electrons into a vacuum from a heated conductor?

The phenomenon described in the question, where electrons are emitted from a heated conductor into a vacuum, is best labeled as thermal emission. This process occurs when the thermal energy provided to the electrons within the conductor allows them to overcome the work function of the material, enabling them to escape into the vacuum.

Thermal emission specifically refers to the emission of electrons due to the heating of a material, distinguishing it from other phenomena involving electron movement or emission. For example, the photoelectric effect involves the emission of electrons as a result of light exposure, not thermal energy. Electron discharge typically refers to the flow of electrons within a medium, like from a charged object to a neutral one, rather than their emission into a vacuum. Electric conduction involves the movement of electrons through a conductive medium in response to an electric field, fundamentally differing from the emission process described in the question.