Absolute zero: The lowest theoretically possible temperature.

Adiabatic: Adiabatic processes are processes that occur without gain or loss of thermal energy (or heat).

Boiling: When the vapor pressure of a material reaches the surrounding pressure, boiling occurs.

Carnot efficiency: The maximum possible efficiency of a heat engine.

Closed system: Closed systems can exchange heat between the system and the surroundings, but matter cannot be exchanged.

Condensation: The process whereby a vapor changes to a liquid.

Cycle: A thermodynamic cycle is defined as a process in which a working fluid undergoes a series of state changes and finally returns to its initial state.

Distillation: Distillation is the process of heating a mixture and condensing the resulting vapor to produce a more pure substance.

Evaporation: A process in which molecules escape from a liquid phase to a gaseous phase.

Heat of vaporization: The amount of heat required to vaporize a certain amount of a liquid at its boiling point with no change in temperature.

Heat engine: Heat engines convert thermal energy into mechanical energy.

Humidity: The mass of water vapor in a fixed total mass of air.

Isolated system: Isolated systems are completely isolated from their surroundings.

Open system: Open systems can exchange both heat and matter with their
surroundings.

System: A thermodynamic system is a part of the universe that can be defined by some boundary or is under consideration.

Thermodynamics: The study of patterns of energy change.

Vapor pressure: The pressure exerted by a vapor in equilibrium with the same substance in the solid or liquid phase.