Proofing (armour)

The proofing of armour is testing armour for its defensive ability, most commonly the historical testing of plate armour and mail (armour). In the early Middle Ages, armour would be classified by the blows it could withstand, being certified as proof against swords, axes, and arrows. As firearms emerged as battlefield weapons, armour would be tested against them, as well, from which came the modern term "bulletproof".