A thermodynamic cycle describes a hypothetical process where a system undergoes a sequence of distinct, reversible or irreversible changes and returns to its initial state, completing a closed loop. These cycles model the conversion of energy, primarily focusing on the transfer between heat and mechanical work. The performance of any such cycle is quantified by its efficiency, which represents the ratio of the net work output to the heat energy input. Different cycles—such as those modeled after steam power plants or internal combustion engines—are mathematical representations used to analyze and design heat engines, providing a fundamental framework for understanding energy conversion in physical systems.