The bias direction of a piece of woven fabric, usually referred to simply as "the bias", is at 45 degrees to its warp and weft threads. Every piece of woven fabric has two biases, perpendicular to each other. The warp is the set of lengthwise threads attached to a loom before weaving begins. ... Weft or woof is the yarn which is shuttled back and forth across the warp to create a woven fabric. ... For the Deep Purple album, see Purpendicular. ...

Woven fabric is more elastic as well as more fluid in the bias direction, compared to the on-grain direction. This property facilitates garments and garment details that require extra elasticity or drapeability or flexibility, such as bias-cut skirts and dresses, piping trims and decorations, bound seams, etc. The word grain has several meanings, most being descriptive of a small piece or particle. ...

A piece of woven fabric is said to be "cut on the bias" when the piece's warp and weft threads are at 45 degrees to its major edges. A garment made of woven fabric is said to be "cut on the bias" when the fabric's warp and weft threads are at 45 degrees to its major seam lines. A seam, in sewing, is the line where two pieces of fabric are held together by thread. ...