It's the feminine form of "fifteen-year-old", also called fiesta de quince años, a celebration of a girl's fifteenth birthday in parts of Latin America. This birthday is celebrated differently from any other , as it marks the transition from childhood to young womanhood.
A dear friend of mine rescued her daughter's dress from 20 years ago. Pulled it from a box all yellowed and stained. It's now pristine white, with hundreds of new hand applied seed pearls, winging it's way to Guatemala for a a very lucky young lady!
