Thermodynamic efficiency measures how well a system converts energy from one form to another, particularly in heat engines. It is defined as the ratio of useful work output to the total energy input. A higher efficiency indicates that more of the input energy is being transformed into useful work, while less is wasted as heat. In practical terms, thermodynamic efficiency helps evaluate the performance of engines, refrigerators, and other energy systems. For example, a steam engine with high thermodynamic efficiency will produce more mechanical work from the heat energy generated by burning fuel, leading to better fuel economy and reduced emissions.