A Smart defense. Can be provided by various game abilities or plot created scenarios. From the Accelerant core rules book:
"You choose one attack of the appropriate type to negate when it strikes you. You can allow an attack to affect you and negate a later attack. Although different verbals are used to indicate the nature of your defense and to add flavor to the game, this defense works the same way as Avoid and Resist. You must call out the defense when it is used."
The primary difference between this ability and an Elude, Guard, or Shield is being able to wait until the right opportunity to activate the defense. If you were struck by a smaller attack, you could forgo expending this defense in favor of using it on a bigger attack from the enemy later on.