The Prusik Knot (sometimes called a triple sliding hitch) is a slide and grip knot. It was developed by Dr. Prusik of the Austrian Mountaineer Club as a means to attach to a vertical rope for climbers. I’ve also read instances where it has been used to climb a mast of a sailboat.
The strength of this knot is that it forms a coil of rope on either side of its loop allowing it to grip when a load is applied in either direction. The climber’s application used a loop being passed inside of itself 3 times to form the knotted loop, and then clipping into a carabineer.
Below are step-by-step pictured instructions for tying this knot…
To visualize the climbing application of this knot, the ends will just be a loop that you pass over the climbing rope (vice rope ends). It’s a very good knot, but has limited applications.