Energy efficiency or efficient energy usage is a goal, aiming to reduce energy consumption by adopting new technology/means. For example, using LED bulbs instead of CFLs for lighting purpose reduces both energy consumption and the cost. Energy efficiency is an important means to handle growing energy demands or for sustainable energy.
Energy Intensity is a quantitative metric for nation’s energy efficiency. For a country, it is calculated as the ratio of the total energy units consumed and the total units of GDP over a calendar year. The lower its value, the better is the energy efficiency. A higher value of energy intensity means more money is being spent on energy to convert it into nation’s GDP, which is bad.