It is the main backbone of a carpet and it consists of yarn strands that stretch from top to bottom (height-wise, vertically). These strands are stretched on the loom before weaving begins. Once the rug is completed and cut from the loom, the ends of the warp make up the fringe. The warp is normally made of wool, cotton or silk.
It is referred to as the collection of knots of yarn that are twisted between the warp strands. The knots are weaved in either the Turkish (Traditional, Ghiordes, Symmetrical) knot, or the Persian (Commercial, Senneh, Asymmetrical) knot. The Turkish knot is a double knot formed by looping the pile yarn across two warp strands and then drawing each end back through the inside of both warps. The Persian knot is a single knot formed by looping the pile yarn through two warp strands and then drawing it back through one. The Turkish knot is more difficult to tie and more durable than the Persian knot.
These are yarn strands that are inserted perpendicular (width-wise, horizontally) to the warp strands, and woven in and out of the warp strands during weaving. It is normally made up of the same material as the warp, but is only visible from the back of the rug. The number of weft strands that pass between the rows of knots are referred to as shoots, and sometimes the weft strands are dyed.
Both edges of a woven rug are covered with overcast (a simple running stitch) or selvaged (finished with a woven band) in order to reinforce the edges, as they are particularly susceptible to wear.