the.com/prom

means A formal dance held by a high school class, typically near the end of the school year, treated as a milestone of teenage social life.

from Short for 'promenade,' which comes from French promener, 'to walk or stroll' — the formal walk or march that opened grand 19th-century balls. American colleges and then high schools borrowed both the walk and the word, and by the early 20th century 'prom' had shrunk from a stately entrance into the whole evening itself.