reactive armor
External modular armor packages used in tanks and other real life modern military vehicles. Reactive armor actively reduces the damage a vehicle equipped with it receives, instead of passively resisting it like traditional armor.
The most common type of reactive armor currently is Explosive Reactive Armor (ERA), which will detonate when penetrated and impair or deflect the incoming projectile. This type of armor appears as tiles or plates fitted on top of the normal armor of the vehicle equipped with it. Once their protective surface is spent they can be removed to save weight.
This system is also featured in several mecha from realistic sci-fi anime and manga.