Longman Dictionary of Contemporary English
WordNet
n. a rally (especially of students) before a game
Wikipedia
Pep rallies or pep assemblies are a gathering of people, typically students of middle school, high school, and college age, before a sports event. The purpose of such a gathering is to encourage school spirit and to support members of the team for which the rally is being thrown. The pep rallies are often very loud and have a lot of excitation to keep all the students excited for the upcoming game and to cheer on the team.
At a pep rally, cheerleaders will often lead in boisterous chants and dance moves intended to get the student body involved and supporting the school's team. Games between competing classes with small prizes may be held. The school's band will often play upbeat music in between demonstrations, and the drumline may play. In the case of a homecoming game, the Homecoming "court" may be chosen and announced. It's a big assembly.
This is also a time for the team captains to let the school know how their team are doing this season. Most schools have pep rallies to honor future and past events.
College basketball teams celebrate the opening of the season with Midnight Madness, an event similar to a pep rally.
Usage examples of "pep rally".
Ever since the pep rally that afternoon two of them had been parked on one side of the gym, next to some bleachers.
The flotilla simply becomes a floating pep rally for one faction of the exile community and a dangerous pep rally at that.
Their talk would seem to indicate they'd been at the pep rally down by the wharf, which would mean they were members of the proletarian party.
It was like a pep rally in the gym, voices and laughter reverberating from floor, ceiling, walls, and the music blaring.
A Republican operative recounted the heyday of the religious right, saying the Robertson campaign was what a Nazi pep rally would have been like.