A soutache is narrow flat decorative braid

Braid

A braid is a complex structure or pattern formed by intertwining three or more strands of flexible material such as textile fibres, wire, or human hair...

, a type of galloon

Galloon

Galloon is a decorative woven trim sometimes in the form of a braid and commonly made of metallic gold or silver thread, lace, or embroidery. Galloon is used in the trim of military and police uniforms, ecclesiastical garments, and as trim on textiles, drapery, and upholstered furniture.-...

, used in the trimming of drapery or clothing. In clothing soutache is used to conceal a seam.

In military uniforms a particular width or color of soutache is used to indicate rank, particularly in a hat. In athletic uniforms a contrasting soutache is used to outline numbers or players' names.

Soutache is often woven of metallic bullion thread, silk, or a blend of silk and wool. In the 20th century soutache began to be woven of rayon

Rayon

Rayon is a manufactured regenerated cellulose fiber. Because it is produced from naturally occurring polymers, it is neither a truly synthetic fiber nor a natural fiber; it is a semi-synthetic or artificial fiber. Rayon is known by the names viscose rayon and art silk in the textile industry...

 and other synthetic fibers.

The term is also used in bookbinding

Bookbinding

Bookbinding is the process of physically assembling a book from a number of folded or unfolded sheets of paper or other material. It usually involves attaching covers to the resulting text-block.-Origins of the book:...

, where a narrow soutache is applied at the top and bottom of a book back to reinforce the spine and provide a barrier to keep dust out of the binding.