"Archer's Knot": https://www.youtube.com/watch?v=vXu3NgWHMvA
A really handy knot where the loop stays fixed /w tension on the standing end, and the working end can be cinched to shrink the loop.
Fun fact: this knot seems to be the complement of the Arbor Knot (https://en.wikipedia.org/wiki/Arbor_knot), where standing end tension cinches the loop & the working end doesn't.
Also, handy rope terminology that really helped me out: https://www.ropebook.com/information/knots/terminology/
@johan Yes! It can be handy when you have a horizontal rope going across something, and you want to add fixed spots where you can hook/hang things on it, so they won't slide around the rope.
I haven't tried this, but I also think you could make a simple little rope ladder by tying these alternating left/right along a vertical rope :)
Det här är en instans för talare av skandinaviska språk. Välkommen!