A sash is a cloth belt

Belt (clothing)

A belt is a flexible band or strap, typically made of leather or heavy cloth, and worn around the waist. A belt supports trousers or other articles of clothing.-History:...

 used to hold a robe

Robe

A robe is a loose-fitting outer garment. A robe is distinguished from a cape or cloak by the fact that it usually has sleeves. The English word robe derives from Middle English robe , borrowed from Old French robe , itself taken from the Frankish word *rouba , and is related to the word rob...

 together, and is usually tied about the waist. The Japanese equivalent of a sash, obi

Obi (sash)

is a sash for traditional Japanese dress, keikogi worn for Japanese martial arts, and a part of kimono outfits.The obi for men's kimono is rather narrow, wide at most, but a woman's formal obi can be wide and more than long. Nowadays, a woman's wide and decorative obi does not keep the kimono...

, serves to hold a kimono

Kimono

The is a Japanese traditional garment worn by men, women and children. The word "kimono", which literally means a "thing to wear" , has come to denote these full-length robes...

 or yukata

Yukata

A is a Japanese garment, a casual summer kimono usually made of cotton. People wearing yukata are a common sight in Japan at fireworks displays, bon-odori festivals, and other summer events. The yukata is also frequently worn after bathing at traditional Japanese inns...

 together. Decorative sashes may pass from the shoulder to the hip rather than around the waist. Sash is an Arabic loanword that was introduced into the English language

English language

English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

 in 1590.
Sashes traditionally form part of formal military attire (compare the sword-belt known as a baldric

Baldric

A baldric is a belt worn over one shoulder that is typically used to carry a weapon or other implement such as a bugle or drum...

, and the cummerbund

Cummerbund

A cummerbund is a broad waist sash, usually pleated, which is often worn with single-breasted dinner jackets . The cummerbund was first adopted by British military officers in colonial India as an alternative to a waistcoat, and later spread to civilian use...

).