1. Baseball. a. a place where relief pitchers warm up during a game.
b. the relief pitchers on a team.
2. Informal. a. a large cell or room, usually next to the courtroom, where prisoners are temporarily held.
b. a large room in an office occupied by many employees.
3. any temporary or crowded quarters, as sleeping quarters in a lumber camp.
4. a pen for a bull or bulls. Also,bull'pen".