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Energy that is derived from traditional resources, such as coal, oil, natural gas, and nuclear power, which are seen by some as environmentally unfriendly. If we're going to keep our planet clean, we need to move away from brown energy and invest in renewable resources, such as wind and solar.
bundle of energy
Someone who is exceptionally energetic, alert, productive, or hyperactive. My kids are always such bundles of energy first thing in the morning. Susan is a bundle of energy! She's already finished two of her essays today and is beginning to work on a third.
a waste of energy
A useless, vain, or redundant effort or action. It turns out the boss had already chosen a direction for the project, so my presentation was a complete waste of energy.
In science, energy converted into a form that is unavailable for work. Today, we'll be studying the unavailable energy in this system.
See also: energy