Refers to a raised pattern in the surface texture of a fabric, that might run with the length of the fabrics, or across; well known ribbed fabrics include corduroy, needlecord, faille, ottoman and repp.
A ribbed fabric is a variation on a plain weave with twisted fibres that form a distinct pattern of either horizontal or vertical hills and channels.
In a warp rib the ribs run the length of the fabric so the ridges that create the ribs are formed by the weft thread as it works across the warps; the weft always floats over three warps and under one, repeated across the width; on the return pass the same threads are worked but the pattern is reversed, so that every fourth warp is held tighter than the ones between.
A weft rib has the ribs running across the fabric width – it is woven in the same manner, adjusted to create ribs that run across of the fabric.
In knitting, ribbing refers to a pattern of alternating rows of knit and pearl sticthes that produces an elastic textile with vertical lines.