Thermodynamic concepts and laws
A key concept in thermodynamic analysis, often abused, is the concept of system. A thermodynamic system is the region or collection of matter in space that is selected for analysis. The concept of system requires the recognition of an environment, which is the space, or system, external to the system of interest. Separating the two systems is the system boundary (frontier), which, in general, is a real or imaginary surface delineating the contour of the system of interest.