A "RAT" on a plane stands for Ram Air Turbine. It is a small turbine that deploys from the aircraft in emergency situations, especially when there is a total loss of primary electrical power or engine failure. The RAT uses the airstream (ram pressure) caused by the plane's movement through the air to spin and generate power. This power is then used to operate essential systems such as flight controls, basic avionics, hydraulic pressure, and flight- critical instruments. The RAT is not designed to power the plane for the entire flight or provide thrust but acts as a critical backup to maintain control of the aircraft during severe system failures. It is typically stored inside the plane's fuselage or wing and automatically deploys when needed. Once deployed, it remains extended until the plane lands safely. This emergency device has played a vital role in real-life incidents such as Air Transat Flight 236 in 2001, US Airways Flight 1549 in 2009 (the "Miracle on the Hudson"), and more recently during the 2025 Air India crash where it deployed before the crash due to system failures. In summary, the RAT on a plane is an emergency power source turbine that helps keep control systems operational when primary sources fail, providing a chance for safe landing in critical situations. It is a lifesaving but little-known component that quietly functions in the background during dire emergencies. If you meant "rat" literally as an animal on a plane, it usually refers to an actual rodent, but in aviation context, RAT usually means Ram Air Turbine. Let me know if you want details about either meaning.