The person should be wearing an evening look, such as a sophisticated and expensive looking dress or suit, with hair, make up if it applies, and accessories to boot.
A black tie affair requires a tuxedo and is a formal affair. It may consist of full dress with white shirt and cumberband or men may now wearing a high necked shirt. Women usually wear a long gown or a fancy formal dress.
A black tie dress code means that men should wear a tuxedo and women should wear a gown one step up from a cocktail dress. Usually for women this means a floor length dress.
