A system is a combination of devices and components connected together by some form of regular interactions to act together and perform a certain function. The system may be physical, biological, economic and the like.
The term control means to regulate, to direct or to command. Thus, a control system may be defined as a combination of devices and components connected or related so as to command, direct or regulate itself or another system.
The part of the system which is to be controlled is given different names, for example, plant, controlled system, process, etc. The control system designer develops a controller that will control the plant or the controlled system.