Definition

The energy required to achieve homolytic bond cleavage (generating radicals).
The symbol ∆H˚ denotes bond dissociation energy under standard conditions, that is, at 1 atm and the compound’s original state of matter.

Explanation

Recall that during a homolytic bond cleavage, the electrons that were bonded initially are returned to the respective molecule in equal amounts, i.e. producing radicals.

Structural reaction scheme for Bond Dissociation Energy
Figure. Bond Dissociation Energy