This is a high-end state-of-the-art ice axe leash from Blue Ice.  One end has a loop that can be girth-hitched to your harness or pack.  The other end has a high spring-tension carabiner to attache to your ice axe.  The leash is an ultralight 80cm elastic sling that stretches up to 135cm when fully extended and is designed to not hinder your movements.