A lady in waiting is a woman who attends a monarch or high ranking noble. Historically, ladies in waiting were members of the nobility themselves, although this is no longer necessarily required. This role has also greatly evolved; most modern ladies in waiting are discreet companions rather than members of a huge court entourage which is designed to impress. A good lady in waiting is said to be intelligent, good natured, and not afraid to offer honest or useful advice to her mistress.
Historically, rulers and members of the nobility have always been surrounded by a court, an entourage of individuals which forms a large collective household. Monarchs were often entertained by members of their court, who would dance, sing, play games, participate in plays, and participate in other diversions. In exchange for their roles as companions, members of the court received special privileges and housing as gifts from the monarch.
Queens and female members of the nobility often had a large entourage of women who would collectively be called ladies in waiting. Although they served their mistresses, they were not servants; they did not clean, cook, or take responsibility for managing the royal household, for example, as servants did historically. Ladies in waiting were typically divided into ranks; ladies of the privy chamber, for example, had access to the private quarters of their mistresses, while maids of honor might be relatives of the noble lady in question.
Several ladies in waiting went on to become important historical figures. Many of them wrote vivid descriptions of life in court, sometimes accompanied by artwork and musical compositions. Some became politically powerful because of their closeness to the monarchy, while others became especially close to the monarchy, as in the case of Anne Boleyn, who later became a monarch herself.
This role continues to be one of great privilege, although most monarchs do not surround themselves with extensive, showy entourages anymore. However, monarchs still need friends and companions, and in general any woman who interacts closely with a female noble is known as a lady in waiting. In some regions of the world, these women also serve ceremonial functions; the Mistress of the Robes in England, for example, oversees the Queen's garments and jewelry and also performs an assortment of traditional tasks at State ceremonies. The Mistress of the Robes is typically also a Duchess, incidentally.