A thermodynamic cycle is a series of processes that a working substance undergoes to convert heat into work or vice versa. This cycle typically involves four main stages: compression, heating, expansion, and cooling. Each stage changes the state of the substance, often represented on a pressure-volume or temperature-entropy diagram. Common examples of thermodynamic cycles include the Carnot cycle, Otto cycle, and Rankine cycle. These cycles are fundamental in various applications, such as in internal combustion engines and power plants, where they help optimize energy efficiency and performance.