A waistcoat or vest is a sleeveless upper-body garment. It is usually worn over a dress shirt and necktie and below a coat as a part of most men's formal wear. It is also sported as the third piece in the traditional three-piece male suit. Any given waistcoat can be simple or ornate, or for leisure or luxury. Historically, the waistcoat can be worn either in the place of, or underneath, a larger coat, dependent upon the weather, wearer, and setting.

Formal wear or full dress is the Western dress code category applicable for the most formal occasions, such as weddings, christenings, confirmations, funerals, Easter and Christmas traditions, in addition to certain state dinners, audiences, balls, and horse racing events. Generally permitted other alternatives, though, are the most formal versions of ceremonial dresses, full dress uniforms, religious clothing, national costumes, and most rarely frock coats. In addition, formal wear is often instructed to be worn with official full size orders and medals.