The Adjustable Bend. A great way of lengthening or shortening two lines tied together. Under a moderate and steady load, the two knots will remain apart. Used in climbing and to string tarps in trees, tie down tents, etc.
The bend was invented by the Canadian climber Robert Chisnall sometime before 1982. More accurately a coupling of two identical knots, the bend is a great way of lengthening or shortening two rope ends tied together.