Introduction:
In control systems, the terms "open loop" and "closed loop" refer to the presence or absence of feedback. These terms are used to describe the structure and behavior of a control system.

Open Loop System:
An open loop system, also known as a non-feedback system, does not have any mechanism to monitor or control the output. It relies solely on the input and the internal dynamics of the system to generate the output. The output of an open loop system is determined by the input pattern and the system's internal characteristics. It does not take into account any external disturbances or changes in the system.

Closed Loop System:
A closed loop system, also known as a feedback system, includes a feedback mechanism that monitors the output and compares it with a desired reference value. The feedback information is then used to adjust the input or the system's parameters in order to reduce the error between the output and the reference value. This feedback loop enables the system to compensate for disturbances, uncertainties, and changes in the system.

Distinction between Open Loop and Closed Loop Systems:
The key distinction between open loop and closed loop systems is the presence of feedback.

Feedback:
Feedback is the process of monitoring the output of a system and using that information to adjust the input or the system's parameters. It provides information about the system's performance and enables corrective actions to be taken. In a closed loop system, feedback is used to continuously compare the output with the reference value and make adjustments to ensure the output matches the desired value.

Importance of Feedback:
Feedback is essential in control systems for several reasons:
1. Stability: Feedback helps in stabilizing the system by detecting and correcting errors or deviations from the desired output.
2. Accuracy: Feedback enables the system to achieve a high level of accuracy by continuously adjusting the input or system parameters to minimize the error between the output and the reference value.
3. Robustness: Feedback allows the system to adapt to changes in the system or external disturbances, ensuring reliable and consistent performance.
4. Flexibility: Feedback provides the ability to change the desired output or reference value, allowing the system to respond to different operating conditions or requirements.
5. Performance Improvement: Feedback allows for optimization of system performance, enabling faster response times, reduced steady-state error, and improved overall system behavior.

Conclusion:
In summary, a closed loop system is distinguished from an open loop system by the presence of feedback. Feedback enables the system to continuously monitor the output, compare it with a reference value, and make necessary adjustments to ensure the desired output is achieved. This feedback loop provides stability, accuracy, robustness, flexibility, and performance improvement in control systems.