Court uniform and dress were required to be worn by those in attendance at the royal court in the 19th and early 20th centuries.
Specifically, court uniform was worn by those holding particular offices (e.g. in the government, the Civil Service, the Royal Household, etc.). A range of office-holders were entitled to wear it, with different grades of uniform specified for different grades of official. It is still worn today on state occasions by certain dignitaries both in the UK and abroad.
Court dress, on the other hand, is a stylized form of clothing deriving from fashionable eighteenth-century wear, which was directed to be worn at court by those not entitled to a court uniform. For men, it comprises a matching tailcoat and waistcoat, breeches and stockings, lace cuffs and cravat, cocked hat and a sword. For women, a white or cream evening dress is directed to be worn, together with a train and other specified accoutrements. Male court dress is still worn today as part of the formal dress of judges and Queen's Counsel, and is also worn by certain Lord Mayors, parliamentary officials, and high sheriffs of counties. Female court dress was at one time required wear for debutantes being presented at court, but it ceased regularly to be worn after the Second World War (when afternoon presentations replaced evening courts).
Precise descriptions, both of court uniform and of court dress, were laid down in an official publication called Dress Worn at Court, which was published by the Lord Chamberlain's Office. The 1937 edition remains authoritative for those rare circumstances in which court uniform or court dress are still required.