Energy

  The capability of doing work; different forms of energy can be converted to other forms, but the total amount of energy remains the same.

  This is broadly defined as the capability of doing work. In the electric power industry, energy is more narrowly defined as electricity supplied over time, express in kilowatt-hours.

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  The capacity for doing work as measured by the capability of doing work (potential energy) or the conversion of this capability to motion (kinetic energy). Energy has several forms, some of which are easily convertible and can be changed to another form useful for work. Most of the world's convertible energy comes from fossil fuels that are burned to produce heat that is then used as a transfer medium to mechanical or other means in order to accomplish tasks. Electrical energy is usually measured in kilowatthours, while heat energy is usually measured in British thermal units (Btu).

  U.S. Dept. of Energy, Energy Information Administration's Energy Glossary

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  The capacity for doing work. Forms of energy include: thermal, mechanical, electrical and chemical. Energy may be transformed from one form into another.

  California Energy Comission. Dictionary of Energy Terms

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  The ability to do work. Stored energy becomes working energy when we use it.

  Solar Electric Glossary