SAE 10W-40 is a type of motor oil that meets the standards set by the Society of Automotive Engineers (SAE). The "10W" indicates its viscosity at low temperatures, meaning it flows like a 10-weight oil in cold conditions. The "40" signifies its viscosity at high temperatures, allowing it to perform like a 40-weight oil when the engine is hot. This oil is commonly used in various vehicles, providing good protection and performance across a range of temperatures. It is suitable for both gasoline and diesel engines, making it a versatile choice for many drivers and mechanics.