Engine efficiency refers to how well an engine converts fuel into useful work or energy. It is typically measured as a percentage, indicating the ratio of useful output power to the energy input from fuel. Higher efficiency means more power is generated from the same amount of fuel, leading to better performance and lower fuel costs. Factors affecting engine efficiency include design, operating conditions, and fuel type. For example, internal combustion engines generally have lower efficiency compared to electric engines, which can convert a higher percentage of energy into motion. Improving engine efficiency is crucial for reducing emissions and conserving resources.