The title refers to diamond gemstones with the highest quality, having, or approaching, the clarity, purity, and perfection of clear water. It is also used to describe an exceptionally beautiful young woman.
In the books, the Berbrooke men were used as comic relief and the Bridgerton girls were never encouraged to marry them or encourage them.
The mansion under construction is Carlton House.
The song playing during the ball is a string arrangement of Arianna Grande's "Thank U, Next."
Although the construction happening on the palace communicates that it was either Buckingham Palace or Carleton House, both of which were not yet completed in 1814, the Royal residence which the Bridgertons and Featheringtons arrive at to be presented before Queen Charlotte is Hampton Court Palace. Hampton Court is the last standing great seat of Henry VIII, and was a particular favorite of other monarchs such as Charles II. Its famous red brick great gateway can be seen in the pilot episode as carriages fill its courtyard before the presentation to the Queen.