Warp and weft are the two thread directions present in every woven textile, rugs included. Warp threads are strung vertically on the loom under tension before weaving begins and run the length of the finished rug; weft threads are woven horizontally across the warp, over and under, row by row.
Why it matters to a buyer
In a hand-knotted rug, knots are tied around pairs of warp threads, with weft threads woven between rows of knots to lock them in place — the warp and weft form the hidden structural grid that the visible pile sits on. In a flatweave rug, warp and weft are the entire visible construction, since there is no pile layered on top. The fiber used for warp and weft (often cotton, for strength and minimal stretch) is a separate choice from the pile fiber.