Evening dress; a standard of dress which is less formal than white tie, consisting of black dinner jacket, and matching trousers, white shirt and black bow tie or, possibly military dress or national costume
If a man is dressed in black tie, he is wearing formal evening dress, which includes a dinner jacket or tuxedo and a bow tie. Most of the guests will be wearing black tie
A black tie event is a formal social event such as a party at which people wear formal clothes called evening dress. a black-tie dinner for former students