Definition of energy:
(physics) a thermodynamic quantity equivalent to the capacity of a physical system to do work; the units of energy are joules or ergs; "energy can take a wide variety of forms"
forceful exertion; "he plays tennis with great energy"; "he's full of zip"
enterprising or ambitious drive; "Europeans often laugh at American energy"
an imaginative lively style (especially style of writing); "his writing conveys great energy"; "a remarkable muscularity of style"
a healthy capacity for vigorous activity; "jogging works off my excess energy"; "he seemed full of vim and vigor"
any source of usable power; "the DOE is responsible for maintaining the energy policy"
the federal department responsible for maintaining a national energy policy of the United States; created in 1977