Bulletproof windows refer to a type of window that is designed and manufactured in such a way as to be resistant to bullets or other forms of projectiles. These windows are typically made from materials like polycarbonate, laminated glass, or bullet-resistant glass, which have high levels of strength and durability. The phrase "bulletproof" is used because these windows can withstand the impact of a bullet without shattering or breaking, providing protection against potential threats such as gunfire.