What is the difference between open-loop and closed-loop control systems?

Open-loop systems operate without feedback - the output has no influence on the control action (e.g., a toaster timer). Closed-loop systems use feedback to compare actual output with desired output and adjust the control action accordingly (e.g., thermostat-controlled heating). Closed-loop systems are more accurate, can compensate for disturbances, but are more complex. Open-loop systems are simpler and cheaper but cannot correct for errors or disturbances.