The adjustable bend is a bend knot (knot that joins two ends of rope/string/cordage together) that has the unique feature of that you are able to tighten it so that the single rope the two ropes make together is shorter, or longer as needed. It was developed by renowned climber Robert Chisnall. This knot can also be tied in webbing.
The adjustable bend has one final feature that makes it very useful to the rock climber climbing with static (non-stretchy) rope. Cut the rope, and tie an adjustable bend with the two ends, and back up each end with an overhand knot to make sure it will not fail. Then, when you fall on the knot, it will lengthen to absorb some of your fall, but then it has to be reset. This is a poor substitute for the usual stretching kind of climbing rope.
The adjustable bend can be used by the camper to create a clothesline with two too short pieces of paracord.