What is efficiency of a heat engine?

The efficiency of a heat engine is defined as the ratio of the work output to the heat input from the high-temperature reservoir. It is expressed as a percentage and indicates how well the engine converts thermal energy into mechanical work. The maximum efficiency is limited by the Carnot efficiency, which depends on the temperatures of the hot and cold reservoirs. In practice, real engines often operate at efficiencies significantly lower than this theoretical maximum due to various losses.