weft -
A hair extension that is glued directly to a person′s natural hair.
Wikipedia
Weft or woof is the yarn which is drawn through the warp yarns to create cloth. In North America, it is sometimes referred to as the "fill" or the "filling yarn". Because the weft does not have to be stretched on a loom in the way that the warp is, it can generally be less strong.
OmegaWiki Dictionary
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weft The horizontal threads (carried by the shuttle during the weaving) that are interlaced through the warp in a woven fabric.