Carabiner

A carabiner (/kærəˈbiːnər/) or karabiner is a specialized type of shackle, a metal loop with a spring-loaded gate used to quickly and reversibly connect components, most notably in safety-critical systems. The word is a shortened form of Karabinerhaken, a German phrase for a "spring hook" used by a carbine rifleman, or carabinier, to attach items to a belt or bandolier.

The carabiner has been improved several times over the decades, making it more lightweight, reliable and durable.

Carabiners are widely used in rope-intensive activities such as climbing, arboriculture, caving, sailing, hot air ballooning, rope rescue, construction, industrial rope work, window cleaning, whitewater rescue, and acrobatics. They are predominantly made from both steel and aluminium. Those used in sports tend to be of a lighter weight than those used in commercial applications and rope rescue. Often referred to as carabiner-style or as mini-biners, carabiner keyrings and other light-use clips of similar style and design have also become popular. Most are stamped with a “Not For Climbing” or similar warning due to a common lack of load-testing and safety standards in manufacturing. While from an etymological perspective any metal attaching link with a spring gate is technically a carabiner, the strict usage among the climbing community specifically refers only to those devices manufactured and tested for load-bearing in safety-critical systems like rock and mountain climbing.

...
Wikipedia