The weft is the second basic component in weaving which turns yarns into fabric. The weft is the yarn placed between warp yarns. The simplest structure is called plain weave or tabby where alternating odd and even warp threads are lifted so that the weft goes over 1 under 1.
Most woven structures warp and weft yarns that are perpendicular to each other which typically creates a 2-dimensional fabric with a rectangular or square interlacement. However, there are specialized looms that can create oblique weaves, triaxial structures as well as undulating effects where warp threads are periodically spread out or crammed to create an undulating appearance in the woven fabric.