Final answer:
The green SOV CLOSED light on the APU control panel and the green APU SOV CLSD message on EICAS signify that the APU fuel shutoff valve is closed, preventing the APU from receiving fuel and operating.
Step-by-step explanation:
The green SOV CLOSED light on the Auxiliary Power Unit (APU) control panel and the green APU SOV CLSD message on the Engine Indication and Crew Alerting System (EICAS) indicate that the APU fuel shutoff valve is closed. This means that the APU, which is a device used to provide power to an aircraft when the main engines are not running, is not receiving fuel and therefore cannot be started or operated. The closure of the shutoff valve is a safety feature which is important to prevent fuel flow when the APU is not intended to be in use or during certain emergencies or maintenance procedures.