Is it just a cow hitch?
It’s basically a cow hitch on the standing part of the rope, but it might have its own name. It creates a nice sliding knot, and it’s easy to tie.
This vector on Shutterstock calls it a hammock knot, but as far as I can tell it doesn’t look like any other hammock knot I can find. The knots I’ve found related to hammocks are more like bowlines, sheet bends, prussik knots, round turn and two half hitches, yosemite bowline, halter hitch…
I thought this tutorial on rigging a shelter called it a taut-line hitch, but actually the taut-line hitch has an extra turn in it.
If you know whether this has a name, let me know!