In not-so-ancient-times (early 1900s and earlier), A woman (girl) would need one of these in order to dance at a ball or other such thing. She would carry this around, usually tied to her wrist. Early in the evening, men (boys) would write their names in the lines of the card, usually numbered. These lines/spaces would corelate do specific pieces of music to dance to. So, if a man signed up for number 5, he would dance with this girl on the fifth song.