WHAT IS A "DANCE CARD"?
A dance card or ballspende, is a card, often decorative, that is used by an attending woman to record with whom she will dance at formal dances and balls. Though originating in the 18th century, they became quite popular in the ballrooms of Vienna and elsewhere in Europe in the 19th century and remained popular at college dances in the U.S. into the 1920s, lingering on into the 1930s in some cases.
The cards were designed to be worn on the wrist (hence the long strings often attached to them) or attached to the gown and would allow the woman to “pencil in” the names of gentlemen seeking a dance.Although there are no formal rules, there are some social conventions which are important to keep in mind. For example, a lady generally does not give more than three dances to the same gentleman unless she is greatly attached to him. It is also traditional to take the last dance with a special someone, leading to the request to “save the last dance for me.” source: http://www.millikin.edu/staley/archives/exhibits/exhibits_dancecards.htm