A cold reservoir is a system or environment that absorbs heat from a working substance in a thermodynamic cycle, allowing the process to continue. It maintains low temperature and facilitates the removal of waste heat from heat engines.
Heat Engine: A device that converts thermal energy into mechanical work by passing through a cyclic process involving heat transfer.
Carnot Cycle: An idealized thermodynamic cycle proposed by Sadi Carnot that provides maximum possible efficiency for a heat engine operating between two temperatures.
Second Law of Thermodynamics: $\text{This law states that entropy in an isolated system always increases over time and processes occur in such a way as to increase total entropy.}$