The term bight is used in knot tying to refer to any curved section, slack part, or loop between the two ends of a rope, string, or yarn. An important concept, the term is used extensively in the description of knots and the discourse of knotting and related subjects.
A familiar practical use is finishing a knot by passing a bight, rather than the end, to make a slipped form of the knot which is more easily untied. The traditional bow knot used for tying shoelaces is simply a reef knot with the final overhand knot made with two bights instead of the ends.
In the bight
The phrase in the bight (or on a bight) means a U-shaped section of line is itself being used to make a knot. Specifically this means that the knot can be formed without access to the ends of the rope. This can be an important property for knots used in situations where the ends of the rope are inaccessible, such as forming a fixed loop in the middle of a long climbing rope.
Many knots normally tied with an end also have a form which is tied in the bight, for instance the bowline and the bowline on a bight. In other cases a knot being tied in the bight is a matter of the method of tying rather than a difference in the completed form of the knot. For example the clove hitch can be made in the bight if it is being slipped over the end of a post but not if being cast onto a closed ring, which requires access to an end of the rope. Other knots, such as the overhand knot, cannot be tied in the bight without changing their final form.
The final tuck of this Slipped buntline hitch is made with a bight rather than the end, making it easier to release after tightening
The bights, in the case of this 3-lead 10-bight Turk's head knot, are the scallops along the perimeter of the knot
The Alpine butterfly knot is a popular climbing knot which is tied in the bight and forms a reliable fixed loop
The Bowline on a bight forms two fixed loops in the middle of a rope
- Clifford W. Ashley, The Ashley Book of Knots (New York: Doubleday, 1944), 597.
- Ashley, 232.
- Ashley, 207.