According to the font of all knowledge (Wikipedia!)...
A carabiner (/k?r??bi?n?r/) or karabiner is a specialized type of shackle, a metal loop with a spring-loaded gate[1] used to quickly and reversibly connect components, most notably in safety-critical systems. The word is a shortened form of Karabinerhaken (or also short Karabiner), a German phrase for a "spring hook"[2] used by a carbine rifleman, or carabinier, to attach items to a belt or bandolier.