Taut-line Hitch
The taut-line hitch creates an adjustable loop that locks under a strain. 
Taut-line hitch - named because the hitch is useful when working with a taut (tight) rope.
The taut-line hitch is invaluable when working a rope that is under a strain.  The loop formed by the taut-line hitch is adjustable, but stays in place when the rope is subjected to a strain because the extra loop causes the hitch to kink itself in place.  This hitch is great when tying a rope around a stake because it can be used to adjust the length of the rope.  For example, when pitching a tent or a canopy, the taut-line hitch allows you to adjust the length of the guy line and stays in place when strained.
How to Tie

Stephen C. Dibler, Last update: 12/19/2002