For some reason this amazingly useful knot has been forgotten. Like many knots, it is stronger than a square knot, but it is unique in that it can always be untied easily, even after it has been loaded heavily. In other words, it will not “jam”. It is also easy to tie and easy to verify.
Supposedly it is called the Rosendahl or “Zeppelin” knot because American airship commander Charles Rosendahl insisted on its use in mooring lines. Airships can put tremendous transient loads on those lines, so they needed strong knots that could still be untied in a hurry.