What type of control system uses feedback from the output to regulate the input?

The correct answer is closed loop. A closed-loop control system actively uses feedback from its output to make adjustments to its input to achieve the desired performance. This feedback helps the system to continuously monitor its output and correct any deviations from the desired setpoint or target.

In contrast, an open-loop control system operates without this feedback mechanism; it processes input commands based purely on predefined instructions without considering the output results. This can lead to inefficiencies or inaccuracies since there is no adjustment made based on the actual output.

While 'feedback loop' is related to how closed-loop systems function, it is a broader term and does not specifically identify the overall category of control systems that include a feedback mechanism as fundamental. The term 'control system' itself is too general and does not denote that feedback is used specifically. Thus, the defining characteristic of needing feedback to regulate input points directly to the closed-loop system.