Motor oil is a lubricant used in internal combustion engines to reduce friction between moving parts. It helps to keep the engine running smoothly by providing a protective layer that prevents wear and tear. Additionally, motor oil helps to cool the engine by carrying heat away from the moving components. There are different types of motor oil, including conventional, synthetic, and blended oils, each designed for specific engine needs. The viscosity, or thickness, of motor oil is measured by a rating system, such as SAE 5W-30, which indicates how well the oil flows at different temperatures. Regular oil changes are essential for maintaining engine health.