A quinceañera is most specifically a birthday celebration.
It marks a girl’s fifteenth birthday, although the event can include formal rituals that make it more elaborate than an ordinary birthday party. Families may arrange a church service, a reception, symbolic gifts, speeches, a formal presentation, and choreographed dances.
Because the celebrant may wear a formal gown and be accompanied by attendants, observers sometimes compare the event with a wedding. That comparison is visual rather than literal: a quinceañera does not marry the celebrant, and its defining occasion is her fifteenth birthday.
It is also distinct from graduation. A graduation recognizes completion of a course of study, while a quinceañera recognizes a life-stage birthday. Families may hold both celebrations in the same year, but the two events have different purposes and traditions.