Weft is the yarn which is shuttled back and forth across the warp to create a wovenfabric. It can also be referred to as woof and in North America, it is sometimes referred to as the "fill" or the "filling yarn.".
The weft is a thread or yarn of spun fibre. The original fibre was wool, flax or cotton. Nowadays, many manmade fibres are used in weaving. Because the weft does not have to be stretched in the way that the warp is, it can generally be less strong.