Materials & Techniques
On a loom, a loop of thread passing around a warp yarn. A group of heddles is lifted (or lowered) together to open a space (shed) for the weft to be passed in weaving. For plain weave on the backstrap loom, every other warp yarn (those under the shed rod) is enclosed by a heddle, which is usually affixed to a heddle rod. On a simple treadle loom, the heddles are mounted in two or more frames called shafts and all the warp yarns pass through heddles on one or another shaft.
Ann Rowe, “Glossary,” in Weaving and Dyeing in Highland Ecuador, edited by Ann Rowe, Laura Miller and Lynn Meisch (Austin: University of Texas Press, 2007): 289-295.