Short answers, pulled from the story.
A maid of honour is a junior attendant to a queen in royal households, ranking below a lady-in-waiting. The role has historically been used in most European royal courts and required the attendant to be unmarried and usually a member of the nobility.
Traditionally a queen regnant had eight maids of honour. Queen Anne Boleyn had seven maids of honour and one mother of maids, and Anne of Denmark's household ordinance of the 20th of July 1603 set provision for six maids.
The six maids of honour at Queen Elizabeth II's coronation were Lady Moyra Hamilton, Lady Anne Coke, Lady Jane Vane-Tempest-Stewart, Lady Mary Baillie-Hamilton, Lady Jane Heathcote-Drummond-Willoughby, and Lady Rosemary Spencer-Churchill. Their principal duty was carrying the trains of the queen's robes throughout the ceremony.
Maids of honour did not always receive a fee or salary beyond board and lodging. In the seventeenth century some received £10 yearly, and others received grants, property leases generating annual rent, or dowries from the monarch. In 1630, Cecilia Crofts gained pensions and income from duty on coal mines near Benwell.
In 1912, King George V granted maids of honour the style of The Honourable, with precedence next after daughters of barons.
The American English term maid of honor, meaning the best friend of a bride who leads her bridal party, derives directly from the royal title maid of honour used in European royal courts.