A system is defined as a collection of interrelated part forming a synergistic whole that jointly perform functions that each part by itself cannot perform. The parts of the systems, also called components or elements, can be thing, or people, or both. Actions of the system elements including interactions between them constitute the processes of the system. Systems can be very simple and constitute of only things. For example, a chair is a physical system that serves the purpose of providing the convenience for sitting. The various components of the chair like its legs, seat, arms, and the back rest are connected to each other to to provide necessary shape, strength, rigidity and other characteristics to the chair, which enable the chair as a whole to serve its purpose. Systems can also be very complex like human body, a manufacturing plant, or a business organization.
The system as a whole receives inputs from sources outside itself, processes these inputs within the system, and transfers the outputs or results of these processes to outside itself. Whatever exists outside the system is described as environment of the system.
System are have boundaries that separate systems from their environment. A system is influenced by its environment and in turn may be influenced by it, but a system does not have direct control over the process in the environment.
Depending on its relationship with the environment, systems are divided in two broad categories - open systems and closed systems. An open system interacts with its environment while a closed system does not. In practical world there are no systems that are absolutely closed. Systems that have relatively limited interaction wit its environment are, therefore, considered closed systems while those with substantial interaction are considered open systems.
For example, the R&D department of a company may have much less interaction wit people outside the department as compared to marketing department. Therefore, we may consider the R&D department organization as a closed system, and Marketing department organisation as an open system.