‘Lounge suit’ is an expression only seen on invitations as a dress code. In conversation the terms dark suit or business suit or possibly business dress or business attire are used. Lounge suits are worn for most business events, both daytime and evening, and for many social events, such as lunches, receptions, dinner, weddings, christenings and funerals. Dark suits are also correct for flat racing, other than events such as Ascot. They may be worn at dinner parties, especially when people come directly from the office, but are less acceptable at country dinner parties.
A three-piece suit consists of a single-breasted jacket, a single- or double-breasted waistcoat and trousers. When wearing a single-breasted waistcoat, the bottom button is always left undone. A two-piece suit consists of single-breasted or double-breasted jacket with trousers (no waistcoat). Belts should not be worn with a waistcoat or double-breasted suit.
A shirt with a turndown (not button-down) collar should be worn with a tie and the top button of the shirt must be done up. The most versatile tie knots are the four-in-hand and the half-Windsor; large Windsor knots should generally be avoided.
For women at evening events, a smart, or cocktail, dress (with sleeves or a jacket) is a suitable choice. For daytime events women should wear a day dress, trouser suit, or skirt and jacket or coat. The overall impression is not quite so formal as when the dress code is morning dress. A neat, tailored look is best for business, with length on or just below the knee.