In the word quinceañera, quince refers to the number 15.
Quince is the Spanish word for fifteen. The related noun quinceañera traditionally describes a girl celebrating her fifteenth birthday, while quince años literally means “fifteen years.” The tilde in the ñ is important because Spanish pronunciation and spelling distinguish ñ from n.
The word’s numerical meaning explains why the celebration is tied to a particular birthday rather than to a general age range. English-language communities commonly use quinceañera for both the honoree and the event, although local usage can differ.
A quinceañera should not be confused with quince, the Spanish word for the quince fruit. They are unrelated meanings that happen to look alike in writing.