Closed-loop control is a fundamental control system methodology that utilizes feedback from a system's output to influence its input, thereby enabling automatic regulation and stabilization. As an academic concept and research area, it investigates the design, analysis, and implementation of systems that continuously monitor their performance against a desired setpoint, generating corrective actions based on the detected error between the actual and desired states. Its key characteristics include inherent robustness against disturbances and parameter variations, enhanced accuracy in tracking desired trajectories, and the capacity for achieving stable and predictable operation in complex dynamic environments, making it indispensable across diverse scientific and engineering disciplines for achieving precise and reliable system control.