| Term | Definition |
| Fossil fuel | A fuel derived from biological material that became fossilized millions of years ago |
| Nonrenewable energy resource | An energy source with a finite supply, primarily the fossil fuels and nuclear fuels |
| Nuclear fuel | Fuel derived from radioactive materials that give off energy |
| Commercial energy source | An energy source that is bought and sold |
| Subsistence energy source | An energy source gathered by individuals for their own immediate needs |
| Energy carrier | Something that can move and deliver energy in a convenient, usable form to end users |
| Turbine | A device with blades that can be turned by water, wind, steam, or exhaust gas from combustion that turns a generator in an electricity-producing plant |
| Electrical grid | A network of interconnected transmission lines that joins power plants together and links them with end users of electricity |
| Combined cycle | A power plant that uses both exhaust gases and steam turbines to generate electricity |
| Capacity | In reference to an electricity-generating plant, the maximum electrical output |
| Capacity factor | The fraction of time a power plant operates in a year |
| Cogeneration | The use of a fuel to generate electricity and produce heat |
| Combined heat and power | The use of a fuel to generate electricity and produce heat |
| Coal | A solid fuel formed primarily from the remains of trees, ferns, and other plant materials preserved 280 million to 360 million years ago |
| Petroleum | A fossil fuel that occurs in underground deposits, composed of a liquid mixture of hydrocarbons, water, and sulfur |
| Crude oil | Liquid petroleum removed from the ground |
| Oil sands | Slow-flowing, viscous deposits of bitumen mixed with sand, water, and clay |
| Bitumen | A degraded petroleum that forms when petroleum migrates to the surface of Earth and is modified by bacteria |
| CTL (coal to liquid) | The process of converting solid coal to liquid fuel |
| Energy intensity | The energy use per unit of gross domestic product |
| Hubbert curve | A bell-shaped curve representing oil use and projecting both when world oil production will reach a maximum and when the world will run out of oil |
| Peak oil | The point at which half the total known oil supply is used up |
| Fission | A nuclear reaction in which a neutron strikes a relatively large atomic nucleus, which then splits into two or more parts, releasing additional neutrons and energy in the form of heat |
| Fuel rod | A cylindrical tube that encloses nuclear fuel within a nuclear reactor |
| Control rod | A cylindrical device inserted between the fuel rods in a nuclear reactor to absorb excess neutrons and slow or stop the fission reaction |
| Radioactive waste | Nuclear fuel that can no longer produce enough heat to be useful in a power plant but continues to emit radioactivity |
| Becquerel (Bq) | Unit that measures the rate at which a sample of radioactive material decays; 1 Bq = decay of 1 atom or nucleus per second |
| Curie | A unit of measure for radiation; 1 curie = 37 billion decays per second |
| Nuclear fusion | A reaction that occurs when lighter nuclei are forced together to produce heavier nuclei |
| Energy conservation | Finding and implementing ways to use less energy |
| Tiered rate system | A billing system used by some electric companies in which customers pay higher rates as their use goes up |
| Peak demand | The greatest quantity of energy used at any one time |
| Passive solar design | Construction designed to take advantage of solar radiation without active technology |
| Thermal mass | A property of building material that allows it to maintain heat or cold |
| Potentially renewable | An energy source that can be regenerated indefinitely as long as it is not overharvested |
| Nondepletable | An energy source that cannot be used up |
| Renewable | In energy management, an energy source that is either potentially renewable or nondepletable |
| Biofuel | Liquid fuel created from processed or refined biomass |
| Modern carbon | Carbon in biomass that was recently in the atmosphere |
| Fossil carbon | Carbon in fossil fuels |
| Carbon neutral | An activity that does not change atmospheric CO2 concentrations |
| Net removal | The process of removing more than is replaced by growth, typically used when referring to carbon |
| Ethanol | Alcohol made by converting starches and sugars from plant material into alcohol and CO2 |
| Biodiesel | A diesel substitute produced by extracting and chemically altering oil from plants |
| Flex-fuel vehicle | A vehicle that runs on either gasoline or a gasoline/ethanol mixture |
| Hydroelectricity | Electricity generated by the kinetic energy of moving water |
| Run-of-the-river | Hydroelectricity generation in which water is retained behind a low dam or no dam |
| Water impoundment | The storage of water in a reservoir behind a dam |
| Tidal energy | Energy that comes from the movement of water driven by the gravitational pull of the moon |
| Siltation | The accumulation of sediments, primarily silt, on the bottom of a reservoir |
| Active solar energy | Energy captured from sunlight with advanced technologies |
| Photovoltaic solar cell | A system of capturing energy from sunlight and converting it directly into electricity |
| Wind energy | Energy generated from the kinetic energy of moving air |
| Wind turbine | A turbine that converts wind energy into electricity |
| Geothermal energy | Heat energy that comes from the natural radioactive decay of elements deep within Earth |
| Ground source heat pump | A technology that transfers heat from the ground to a building |
| Fuel cell | An electrical-chemical device that converts fuel, such as hydrogen, into an electrical current |
| Electrolysis | The application of an electric current to water molecules to split them into hydrogen and oxygen |
| Smart grid | An efficient, self-regulating electricity distribution network that accepts any source of electricity and distributes it automatically to end users |
| Oxygenated fuel | A fuel with oxygen as part of the molecule |
| Cellulosic ethanol | An ethanol derived from cellulose, the cell wall material in plants |
