1. a. dynamic quality <narrative energy>

b. the capacity of acting or being active <intellectual energy>

c. a usually positive spiritual force <the energy flowing through all people>

2. vigorous exertion of power : effort <investing time and energy>

3. a fundamental entity of nature that is transferred between parts of a system in the production of physical change within the system and usually regarded as the capacity for doing work

4. usable power (as heat or electricity); also : the resources for producing such power