|Generic diagram of an economic cycle (or business cycle). |
In 1946, Wesley Mitchell defined an economic cycle is as follows: 
“Business cycles are a type of fluctuation found in the aggregate economic activity of nations that organize their work mainly in business enterprises: a cycle consists of expansions occurring at about the same time in many economic activities, followed by similarly general recessions, contractions, and revivals which merge into the expansion phase of the next cycle; in duration, business cycles vary from more than one year to ten or twelve years; they are not divisible into shorter cycles of similar characteristics with amplitudes approximating their own.”
In short, an economic cycle refers to one expansion stroke followed by one contraction stroke of one work cycle of an economic system.
In principle, economic cycles, being work cycles of system of economically bound human molecules, should be quantified via construction of indicator diagrams, in the framework of the James Watt and Emile Clapeyron graphical style of pressure-volume work calculation methodology of Carnot cycles.
In human thermodynamic terms, one day constitutes one heat cycle of an economic system of humans, wherein the working body of an economy is first put in contact with a hot body (day sky), which creates an expansion stroke, followed by contact with a cold body (night sky), which creates a contraction stroke.
Daily heat cycles are initiated by the coupling of the spin of the earth to the spin of the sun to the spin of the Milky Way; all of which is in trajectory to the great attractor at a speed of about 600 kilometers per second.
In some yet clarified way, daily heat cycles, which are integrated in the context of seasonal cycles (four seasons per year), give rise to economic cycles (12-years per cycle, on average), which in turn are connected to architectural cycles (architecture) (100-years per cycle, on average), all of which in turn give rise to the cycles of the rise and fall of civilizations (1,000-years per cycle, on average), which in turn are connected to the mass extinctions, which are known to occur cyclically ever 26-million years (sloughing hypothesis). 
A few writers, such as American philosopher Charles Dýke (1994) or Russian bioelectrochemist Octavian Ksenzhek (2007), to cite two examples, have touched on the topic of discussing economic cycles in the context of thermodynamic formalism.  Others to have touched on this topic include: Borisas Cimbleris, John Bryant, and Jurgen Mimkes.
1. Burns, Arthur F and Mitchell, Wesley C. (1946). Measuring Business Cycles. New York: National Bureau of Economic Research.
2. (a) Thims, Libb. (2007). Human Chemistry (Volume One). Morrisville, NC: LuLu.
(b) Thims, Libb. (2007). Human Chemistry (Volume Two). Morrisville, NC: LuLu.
3. (a) Dýke , Charles. (1994). “From Entropy to Economy: A Thorny Path”, in: Economic and Thermodynamics (ch. 11: 207-38; economic cycles, pg. 231), edited by: Peter Burley and John Foster. Kluwer Academic Publishers.
(b) Ksenzhek, Octavian. (2007). Money: Virtual Energy: Economy Through the Prism of Thermodynamics (economic cycles, pg. 103). Universal Publishers.
4. Business cycle – TransTutors.com.
● Business cycle – Wikipedia.