Heat

Heat
A glowing-hot metal bar showing incandescence, the emission of light due to its temperature, is often recognized as a source of heat.
Common symbols	${\displaystyle Q}$
SI unit	joule
Other units	British thermal unit, calorie
In SI base units	kg⋅m2⋅s−2
Dimension	${\displaystyle {\mathsf {L}}^{2}{\mathsf {M}}{\mathsf {T}}^{-2}}$

In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not contain heat. Nevertheless, the term is also often used to refer to the thermal energy contained in a system as a component of its internal energy and that is reflected in the temperature of the system.

Calorimetry is measurement of heat by its effect on the states of interacting bodies, for example, by the amount of ice melted or by change in temperature of a body.

In the International System of Units (SI), the unit of measurement for heat is the joule (J).