In weaving, the warp is the set of lengthwise yarns through which the weft is woven. Each individual warp thread in a fabric is called a warp end. Warp means "that which is thrown across" (Old English wearp, from weorpan, to throw, cf. German werfen, Dutch werpen).
Warp is spun fibre. The spin of the fiber can be in either an "s" twist or a "z" twist. These twist directions make yarn that is similar to hands; each the reverse of the other. Initially the fibre would have been wool or flax (which is known as linen when spun). These fibres provided a strong enough thread to be held under tension as the warp. With the improvements in spinning technology during the Industrial Revolution, it became possible to make cotton yarn of sufficient strength to be used as the warp. Later, artificial or man-made fibres such as nylon or rayon were employed. The weft is the yarn that is woven back and forth through the warp to make cloth.