Loop Sling
Also: Shooting Sling
A sling looped around the support arm to lock the rifle tightly into the body, steadying unsupported field positions.
A loop sling is a shooting sling configured so a loop passes around the support arm above the bicep, putting the strap under tension between the arm and the forward sling swivel. That tension pulls the rifle firmly back into the shoulder and removes much of the muscular wobble that plagues unsupported holds, which is why loop slings remain a fixture in disciplines built on positional marksmanship.
The technique pays off most in the steadier field positions such as prone, sitting, and kneeling, where the support elbow has something to settle against. It is harder to use effectively in offhand, where there is no ground contact, but in any case a properly adjusted loop becomes a core element of position-building for the rifleman working without a bipod or bag.