The basic thermodynamic cycle of the normal four-stroke internal combustion engine: isentropic compression, constant-volume heat addition, isentropic expansion, and constant-volume heat rejection.

(business) The business cycle from startup of operations to the profit; from obtaining the raw material, through designing and production, to the distribution and profits.

The physical cycle of carbon through the Earth’s biosphere, geosphere, hydrosphere and atmosphere that includes such processes as photosynthesis, decomposition, respiration and carbonification.

(physics) A thermodynamic cycle used as an ideal standard for the comparative performance of heat engines.

Alternative spelling of sulfur cycle

(chemistry, biochemistry) the natural cycle which includes the mineralization of organic sulfur to sulfide, oxidation of this to sulfate, and reduction of this to sulfide followed by microbial incorporation of this into organic compounds

The recurring cycle of physiological changes in the uninseminated females of some animal species that is associated with reproductive fertility; especially the cycle in a human woman.

The natural cycle of evaporation of water from the oceans etc, and subsequent condensation and precipitation as rain and snow

(biology) A form of viral reproduction involving the fusion of the nucleic acid of a bacteriophage with that of a host, followed by proliferation of the resulting prophage

(biology) The normal process of viral reproduction involving penetration of the cell membrane, nucleic acid synthesis and lysis of the host cell