In thermodynamics, heat Q is a transfer quantity that may be defined as the energy which, exchanged by a system, has the effect of modifying its temperature (sensible heat) or inducing a change of state (latent heat). [1] Heat can also be defined as the process of energy transfer (conduction, convection, or radiation), energy in transit, or a flow of energy from one body or system to another as a result of a difference in temperature. [2] In differential terms, dQ is an amount of energy transferred as a result of an interaction between two systems differing in temperature. [3]

Social systems
In human thermodynamics, the definition of heat is the same, however, the terminological transfer and the understanding of generalized state terms, such as "energy" or temperature", and conceptions such as "system", e.g. social system, or "latent heat" used in reference to human social systems is a new area of research. How does the sexual heat of reproduction, for instance, related to the definition of heat as energy in transfer? There are many who will argue that the term "heat" used in reference to human life processes is only metaphor. When human systems are defined as consisting of substrate-attached systems of human molecules, however, according to which heat from the sun falls through a temperature gradient to the body of the cold night sky and thereby drives the daily production of human work, the standard definition of heat finds clarification.

Further reading
● Kelland, Philip. (1837). Theory of Heat (182 pgs). London: John W. Parker.
● Maxwell, James C. (1872). Theory of Heat (313 pgs). London: Longmans, Green, and Co.
● Preston, Thomas. (1894). Theory of Heat (719 pgs). London: MacMillan and Co.

References
1. Perrot, Pierre. (1998). A to Z of Thermodynamics, Oxford: Oxford University Press.
2. (a) Daintith, John. (2005). Oxford Dictionary of Science. Oxford University Press.
(b) Schroeder, Daniel V. (2000). An Introduction to Thermal Physics, (pg. 18). Addison Wesley Longman.
(c) Baierlein, Ralph. (1999). Thermal Physics, (pg. 21). Cambridge University Press.
3. Gyftopoulos, Elias P. and Berretta, Gian-Paolo. (2005). Thermodynamics - Foundations and Applications, (pg. 226). New York: Dover.