I’d call that a mooring loop, and the loop part goes around the post. I tie up my horse with that and I’ve done it for so long, I don’t really think about how I do it.

You put the line around the post, twist the long side (halter side) so you make a loop, and pass a loop of the tag end through it, then drop the tag end through the second loop. If the horse pulls, it tightens up both loops but you can pull the tag end out and it comes undone.