Engine 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 minimizes wear and tear. Additionally, engine oil helps to cool the engine by carrying heat away from critical components. There are different types of engine oil, including conventional, synthetic, and blended oils, each designed for specific engine requirements. Regularly checking and changing engine oil is essential for maintaining engine performance and longevity, as dirty or low oil can lead to serious engine damage.