What is a dance card and when did they stop being used?

https://en.wikipedia.org/wiki/Dance_card

A dance card "is used by a woman to record the names of the gentlemen with whom she intends to dance each successive dance at a formal ball."

"In modern times 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". Conversely, someone's "dance card is full" implies that even though they may be interested, they have no time for another person."

"U.S. Air Force aircrews in general, and those involved in flight tests in particular, use the term to describe the first card in a "deck" of flight or test maneuver cards."

So a dance card is a card for women dancing at a ball, an expression or a "term to describe the first card in a "deck" of flight or test maneuver cards".

They did not stop being used (you could host a dance this weekend and hand out dance cards if you want to), but they went out of fashion when dances stopped being a formal social event for the upper class, sometime after WW1.

dancecard.com/History/history.html no longer exists