A defense. Can be provided by various game abilities or plot created scenarios. From the Accelerant core rules book:
"You are affected by the attack in question, but the effect has been mitigated, lessened, or changed entirely. The actual reduction is determined by the skill or ability that allows you to use this defense. Absorb often indicates that the attack had a different effect entirely. The verbal for this defense might be followed by "to" and the modified effect such as "Absorb to Heal 2". You must role play the new effect appropriately."
This effect is only slightly different than a Reduce. It is generally used to manipulate an attack into something else (probably a benefit). A good example would be a lava based creature absorbing a Fire attack and being healed by it rather than negating it.