A thermodynamic system is a specific portion of matter or space that is being studied in thermodynamics, the branch of physics that deals with heat and energy transfer. Systems can be classified as open, closed, or isolated based on how they interact with their surroundings. An open system can exchange both energy and matter, while a closed system can exchange only energy. An isolated system does not exchange either. The boundaries of a thermodynamic system can be real or imaginary, helping to define what is included in the analysis. Understanding these systems is crucial for studying processes like heat engines and refrigerators, which rely on energy transformations to perform work or transfer heat.