What term is used for lightweight ammunition designed specifically for penetrating armored targets?

The term used for lightweight ammunition specifically designed to penetrate armored targets is "armor-piercing." This type of ammunition is engineered with a hardened core that allows it to effectively penetrate the protective layers of armored vehicles, body armor, and similar protective materials. The design often incorporates materials like tungsten or steel, which provide a balance between weight and penetrative capability, ensuring that the projectile can maintain sufficient velocity and force upon impact to breach armor.

In the realm of munitions, other terms such as high explosive refer to ammunition primarily designed to create massive explosive effects rather than penetrate armor. A tandem round usually consists of two projectiles, where the first is intended to initiate a countermeasure or reactive armor deterrent, while the second follows to penetrate the main armor. Fragmentary ammo is designed to disburse shrapnel over a wide area, maximizing damage to personnel and unarmored targets rather than focusing on penetrating armor specifically. Therefore, armor-piercing ammunition stands out clearly as the correct answer in the context of its intended function against armored threats.