What is "herringbone stitch"

Herringbone \Her"ring*bone`\ (h[e^]r"r[i^]ng*b[=o]n`), a. Pertaining to, or like, the spine of a herring; especially, characterized by an arrangement of work in rows of parallel lines, which in the alternate rows slope in different directions.

Herringbone stitch, a kind of cross-stitch in needlework, chiefly used in flannel.
--Simmonds.

A herringbone stitch is a needlework stitch used in embroidery, knitting and crochet. It is so named as it resembles the bones extending from the spine of a herring fish. In knitting, it is a stitch that creates a fabric pattern closely resembling a herringbone pattern, or herringbone cloth.

A knitted herringbone stitch creates a firm fabric "similar to a woven in appearance and elasticity". A heavyweight fabric can be made with variations of the herringbone stitch, such as the herringbone twist stitch, which can be worked in either one or two colours; both versions are suitable for experienced knitters.