A thermodynamic cycle is a series of processes that a system undergoes, returning it to its initial state. These cycles are essential in understanding how engines and refrigerators work. For example, in a car engine, the Otto cycle describes how fuel is burned to produce power, which then drives the vehicle. In a thermodynamic cycle, energy is transferred in various forms, such as heat and work. The Carnot cycle is a theoretical model that helps us understand the maximum efficiency possible for heat engines. By studying these cycles, engineers can design more efficient machines and improve energy use in everyday applications.