Bulletproof/ˈbʊlɪtpruːf/ Definition 1 of 2Pro Tip 1/3Physical Protection Refers to actual items that provide safety from physical threats like gunfire. The security guard wore a bulletproof vest. Pro Tip 2/3High Durability Suggests very strong materials or structures, not just standard ones. The bank installed bulletproof windows. Pro Tip 3/3Not Absolute While strong, it doesn't mean indestructible; high-caliber rounds can be an exception. The door was virtually bulletproof.