the.com/bulletproof vest

means A protective garment with layers of tough fiber or plates designed to stop or slow bullets and reduce injury from gunfire.

from The 'vest' part is old — a sleeveless garment going back to French veste and Italian veste, rooted in Latin vestis, 'clothing.' 'Bulletproof' is a straightforward 17th/18th-century compound: bullet (a small ball, from French boulette, little ball) plus proof, in the old sense of 'tested and found resistant,' the same 'proof' in 'waterproof' or 'fireproof.' Early armor tested against gunfire was literally shot at to prove it — survive the shot, earn the name. Modern soft body armor, woven from synthetic fibers, dates to the 20th century, but the word's bones are much older.