Energy conservation is the effort made to reduce the consumption of energy by using less of an energy service.

Energy consumption is the amount of energy or power used.

Energy conversion efficiency (η) is the ratio between the useful output of an energy conversion machine and the input, in energy terms.

An energy crisis is any significant bottleneck in the supply of energy resources to an economy.

Energy crops are low-cost and low-maintenance crops grown solely for energy production by combustion (not for food).

The amount of energy stored in a given system or region of space per unit volume.

Energy development is the field of activities focused on obtaining sources of energy from natural resources.

Energy distance is a statistical distance between probability distributions.

An energy drink is a type of drink containing stimulant compounds, usually caffeine, which is marketed as providing mental and physical stimulation (marketed as "energy", but distinct from food energy).

Energy economics is a broad scientific subject area which includes topics related to supply and use of energy in societies.

The goal to reduce the amount of energy required to provide products and services and can also reduce effects of air pollution.

The CO2 emission index used to evaluate the vessel design. The index compares theoretical CO2 emissions and transport work of a vessel (gCO2 /tnm).

Energy efficiency gap refers to the improvement potential of energy efficiency or the difference between the cost-minimizing level of energy efficiency and the level of energy efficiency actually realized.

Energy Efficiency Operating Indicator “EEOI”, developed by the IMO in order to allow shipowners to measure the fuel efficiency of a ship in operation. It is a carbon intensity indicator “CII” and represents the demand for transport work.

A measure of cooling efficiency for heat pump equipment, expressed as the cooling energy removed from the space (Btu) divided by the electric energy consumed to provide that cooling (W).

In a typical power distribution grid, electric transformer power loss typically contributes to about 40-50% of the total transmission and distribution loss.

Energy elasticity is a term used with reference to the energy intensity of Gross Domestic Product.

Energy energetics is the scientific study of energy in general

Energy engineering or Energy Systems Engineering is a broad field of engineering dealing with energy efficiency, energy services, facility management, plant engineering, environmental compliance, sustainable energy and renewable energy technologies.

Energy flow is the flow of energy through living things within an ecosystem.