Dance card

A dance card (also known by its German-language name, Ballspende, plural Ballspenden) is used by a woman to record with whom she will dance each successive dance at a formal ball. They appear to have originated in 18th century, but their use first became widespread in 19th century Vienna, especially at the massive balls during Fasching before Lent.

An actual dance card is typically a booklet with a decorative cover, listing dance titles, composers, and the person with whom the woman intended to dance. Typically, it would have a cover indicating the sponsoring organization of the ball and a decorative cord by which it could be attached to a lady's wrist or ball gown. From the 19th century until World War I, dance cards for the elite of Austria-Hungary were often very elaborate, with some even incorporating precious metal and jewels.

Pictures

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  Dance card cover depicting 1884 U.S. presidential tickets
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  Inside of 1884 dance card

Metaphorical usage

Nowadays, the expression "dance card" is often used metaphorically, as when someone says "pencil me into your dance card," meaning "find some time to spend with me."

Among the polyamorous, a person's "dance card" is their set of romantic/sexual partners. "How full is his dance card?" means "Is he open to more relationships?"