A Luenberger observer is a type of state observer used in control systems to estimate the internal state of a dynamic system. It works by combining the system's output measurements with a mathematical model of the system to provide real-time estimates of unmeasured states. This is particularly useful in systems where not all states can be directly observed. The observer uses feedback from the output to correct its estimates, ensuring that the estimated states converge to the actual states over time. This technique is widely applied in various fields, including engineering, robotics, and automotive systems, to enhance system performance and reliability.