A carabiner 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. 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 rescuing, 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.