A ground power unit (GPU) is a device used to provide electrical power to an aircraft while it is on the ground. This allows the aircraft to operate its systems, such as lighting and air conditioning, without needing to run its engines. GPUs are essential for maintaining the aircraft's electrical systems during pre-flight checks and boarding. Ground power units can be mobile or stationary and are typically found at airports. They connect to the aircraft through a power cable, supplying the necessary voltage and frequency. This helps reduce fuel consumption and emissions by minimizing engine use while on the ground.