This is a term used in lots of sports, football included, defined as the official manifest of players on the team. In the NFL, teams are allowed to have fifty-three men on their roster, though only forty-six are allowed to be active for any given game. The team is made up of three divisions: offense, defense, and special teams. Each segment must start eleven players when called to play. A team may substitute any or all of its players during breaks in the game.
During the preseason, teams are allowed to have much larger rosters so they may try out many different players. The rosters are allowed to bulge and sometimes reach as many as seventy players. This requires that the team cut players they do not want on their permanent roster for the regular season. The NFL regulates when the date by which all cuts must be made and rosters finalized. This typically occurs between the last preseason game and the first regular season game, though some teams make decisions earlier than the deadline.