A pep rally is a gathering of people, typically students of high school 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.
At a pep rally, cheerleaders will often lead in boisterous chants 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.
This is also a time for the team captains to let the school know how their team is doing this season.