Meaning of "energy of activation"

the minimum quantity of energy that the reacting species must possess in order to undergo a specified reaction.

ac·ti·va·tion energy

ăk′tə-vā′shən

activation energy

(ăk'tə-vā'shən)
The least amount of energy needed for a chemical reaction to occur. For example, if a match is marked on the side of a matchbox, the activation energy is obtained, in the form of heat, necessary for the match's chemicals to ignite.