Prom's a weird word, isn't it? I mean, like, who would name it that? Plus it's the only one-syllable word with a PR that I can think of, except for prime. So yeah, a Prom is a dance or something where high schoolers get all dressed up, dance for a bit, get drunk and have sex. Nobody that has anything to do with Bro-Op has ever been to a Prom, so this information may not be accurate.
A Prom usually occurs at the end of the spring season, coinciding with the High Schooler's mating period. Occasionally, people will go to a Prom without a date and will leave a Prom as a virgin, these are what are referred to as Squares by the Prom Council.