What does the engine oil grade 10w40 mean?

[McKylie]

Engine oil grade 10w40 indicates a minimum applicable temperature of -25 degrees Celsius, with a kinematic viscosity of 14.5cst at 100 degrees Celsius. The number 10 represents the oil's minimum applicable temperature, W stands for Winter, and 40 denotes the oil's high-temperature viscosity. The number before W in the grade indicates the oil's low-temperature fluidity - the smaller the number, the better the low-temperature fluidity. The number after W represents the oil's viscosity grade at 100℃ - the larger this number, the better protection the oil provides for the engine at high temperatures. Engine oil is a substance enhanced with additives in base oil, mainly containing anti-wear additives, detergents, dispersants, and multi-grade oil viscosity index improvers, used for lubricating internal combustion engines.