A cummerbund is simply a belt-like pleated article of clothing that is typically worn around the waist as part of the attire for a formal event – i.e. commonly worn with a tux. The cummerbund was first adopted by British colonial officers who ventured off into India. This article of clothing became popular amongst these officers as an alternative to the waistcoat (more commonly known as the vest). The word itself originates from the Persian language (In Farsi, Cummerbund simply means belt – the literal translation would be a band that covers the waist area).
The pleats in a cummerbund usually face upwards. The reason for this is that in the olden days, the pleats used to be used for collecting ticket stubs and other articles. Nowadays, you can have cummerbunds in different colors but you usually want to have your bow tie and cummerbund match. Another thing to note is that a cummerbund is worn with a bow-tie rather than a regular neck-tie.