What is the Definition of Energy?

The Blessed Buddha once said:
What, Bhikkhus, is the ability of Energy? Here, Bhikkhus, the Noble Disciple lives
with energy aroused for the elimination of all disadvantageous mental states, and
for gaining a firm foundation in all advantageous states.
He is determined, resolute in all his efforts, not evading any good opportunity to
train advantageous mental states. That enthusiasm is called the ability of Energy. 
Source: Samyutta Nikāya V 48

Without Energy, there arises no advantageous behaviour (good action = good kamma).
Without any advantageous behaviour doing good, neither is there any good result...
No cause, produces no effect! Therefore: Raise up, and stir up your own elevation!

For details on the Enthusiastic Ability of Energy see:
https://What-Buddha-Said.net/drops/III/The_Definition_of_Energy.htm
https://What-Buddha-Said.net/drops/III/The_Arising_of_Energy.htm
https://What-Buddha-Said.net/drops/III/The_Ability_of_Energy.htm
https://What-Buddha-Said.net/drops/III/The_Origin_of_Energy.htm
https://What-Buddha-Said.net/drops/Enthusiastic_is_Energy.htm
https://What-Buddha-Said.net/drops/III/Power_of_Energy.htm
https://What-Buddha-Said.net/drops/III/Ballanced_Energy.htm
https://What-Buddha-Said.net/drops/III/The_Chief_Hero.htm
https://What-Buddha-Said.net/drops/III/Energetic_Effort.htm
https://What-Buddha-Said.net/drops/III/Avoiding_Effort.htm
https://What-Buddha-Said.net/drops/III/Feeding_Energy.htm
https://What-Buddha-Said.net/drops/III/Energy_Viriya.htm
https://What-Buddha-Said.net/drops/III/Dual_Energy.htm