The Double Fisherman's Bend also known as the Double Fisherman's Knot. It would see that this particular bend comes with two names, depending on which book you get your information from. Geoffrey Budworth mentions this in his book as the Fisherman's Knot.
in Art of Knotting and Splicing, by Day; United States Naval Institute , the single not version is known as the Fisherman's Knot, the Lover's knot, the Waterman's Knot and the Water Knot. However, when tied with a double turn as shown in the video (or an additional third turn), then this is also known as the Grapevine Knot.
The Double Fisherman's Bend is a great way of joining two lines together. However, it is said that this bend can be prone to jamming if heavily loaded.
Another great use for the Double Fisherman's Knot is when you want to make a lanyard or bracelet that can easily be adjusted by adding or releasing tension on the Double Fisherman's Bend. Channel Handle: @KnottingKnots