"..I wonder what a Leap Year dance was?"
An excuse to get drunk and hit on woman?
OK, seriously - also known as "Sadie Hawkins Day":
"There was a time when you could attend a Leap Year Ball
throughout the whole Leap Year. In some cases, the event
gave women the opportunity to ask a man, of her choice,
for his hand in marriage.
Leap Year Dances were common as well. Here, a woman
may do the asking for a dance. The women attending either
a Leap Year Ball or a Leap Year Dance may ask her man
to marry her. It is "OK" for a woman to ask in a Leap Year.
If a man declines a marriage proposal, in a Leap Year, he
must provide her with a silk dress and a kiss on the cheek.
Often referred to as Sadie Hawkins Day, February 29 is
Leap Day. Sadie Hawkins Day is November 15th. The only
similarities they share are that the girl does the asking."
http://www.leapyearday.com/LeapYearBalls.htm