Free energy is the maximum amount of work that a thermodynamic system can perform in a process at constant temperature, and its sign indicates whether a process is thermodynamically favorable or forbidden.

Thermodynamic equilibrium is an axiomatic concept of thermodynamics.

A thermodynamic cycle consists of a linked sequence of thermodynamic processes that involve transfer of heat and work into and out of the system, while varying pressure, temperature, and other state variables within the system, and that eventually returns the system to its initial state.

A thermocouple is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction.

A thermocline is a thin but distinct layer in a large body of fluid in which temperature changes more drastically with depth than it does in the layers above or below. In the ocean, the thermocline divides the upper mixed layer from the calm deep water below.

Thermal treatment is any waste treatment technology that involves high temperatures in the processing of the waste feedstock.

Thermal shields protect structures from extreme temperatures and thermal gradients by either thermal insulation or radiative cooling, which respectively isolate the underlying structure from high external surface temperatures, while emitting heat outwards through thermal radiation.

Thermal shock is a type of rapidly transient mechanical load.

Thermal runaway describes a process that is accelerated by increased temperature, in turn releasing energy that further increases temperature.

Opposite to Thermal conductivity, a meaure of a substance ability to resist heat flow.

Electromagnetic radiation generated by the thermal motion of particles in matter.

Heat energy that is converted to electricity. Usually water is heated into steam which is used to drive turbines.

A thermal-neutron reactor is a nuclear reactor that uses slow or thermal neutrons.

A thermal neutron is a free neutron with a kinetic energy of about 0.025 eV (about 4.0×10−21 J or 2.4 MJ/kg, hence a speed of 2.19 km/s), which is the most probable energy at a temperature of 290 K (17 °C or 62 °F).

In building design, thermal mass is a property of the mass of a building which enables it to store heat, providing "inertia" against temperature fluctuations.

Thermal insulation is the reduction of heat transfer between objects in thermal contact or in range of radiative influence.

Thermal hydraulics (also called thermohydraulics) is the study of hydraulic flow in thermal fluids.

Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.

A thermal energy storage tank is a naturally stratified thermal accumulator that allows the storage of chilled water produced during off-peak time, to use this energy later during on-peak time to chill steam turbine inlet air and increment its power output.

Thermal engineering is a specialized sub-discipline of mechanical engineering that deals with the movement of heat energy and transfer.