A thermodynamic system is a portion of space with defined boundaries that separates it from its surroundings/01%3A_Systems_and_Variables/1.01%3A_Thermodynamic_Systems). It can be a body of matter and/or radiation that can be studied using the laws of thermodynamics. A thermodynamic system may be an isolated system, a closed system, or an open system. The physical condition of a thermodynamic system at a given time is described by its state, which can be specified by the values of a set of thermodynamic state variables. A thermodynamic system is in thermodynamic equilibrium when there are no macroscopically apparent flows of matter or energy within it or between it and other systems.

There are three types of thermodynamic systems: open, closed, and isolated. An open system can exchange both energy and matter with its surroundings, while a closed system can exchange energy but not matter with its surroundings. An isolated system cannot exchange either energy or matter with its surroundings.

Thermodynamic systems can be found in various forms, such as engines, refrigerators, air-conditioners, and even ecosystems. The system which involves the processing of heat and converting it to useful work involves thermodynamic processes. When we examine a thermodynamic system, we ignore the difference in behavior from place to place inside the system for a given moment. In other words, we concentrate on the macroscopic properties of the system, which are the averages of the microscopic properties of all the molecules or entities in the system.