Why is a controlled system called a plant in control theory?

In control theory, the term "plant" is used to describe the system that is being controlled. This terminology originates from the field's historical roots in engineering, where the physical equipment, machinery, or industrial facilities—such as a chemical factory or power station—were referred to as a "plant".12

In the context of mathematical models, the plant represents the process whose internal dynamical state is being regulated. By defining the system as a plant, control theorists can focus on the mathematical quantification of its state—often expressed as a state vector—to determine how external inputs and control actions will influence its future evolution. While the specific physical nature of the plant may vary widely, the mathematical principles used to control it remain consistent across different applications.1