- In the manufacture of cloth, warp and weft are the two basic components in weaving to transform thread and yarn into textile fabrics. The vertical warp yarns are held stationary in tension on a loom (frame) while the horizontal weft (also the woof) is drawn through (inserted) over and under the warp thread. In the terminology of weaving, each warp thread is called a warp end; a pick is a single weft thread that crosses the warp thread, synonymous terms are fill yarn and filling yarn.