Bullpen (disambiguation)

A bullpen or bull pen may refer to:


 * Literally, a pen or enclosure for bulls
 * In baseball, the bullpen, an area for pitchers to warm up, also the location of relief pitchers
 * A fortified ridge at the Siege of Port Hudson
 * Broadly, any group of people kept together or in reserve for a common goal, such as the staff of Marvel Comics' Bullpen Bulletins

Open areas holding large groups of people, such as:
 * The bull pen or bull system, where Australian waterfront workers' under the Dog collar act were hired for the day
 * Temporary prison-like areas in the United States for miners arrested for trying to organize into unions
 * An open plan office layout, especially that of local law enforcement
 * The fan zone of NRG Stadium
 * A round pen with solid-walled sides for training horses
 * A holding cell that contains a large number of prisoners
 * A prison yard or open area where prisoners are held
 * An open area in a prison camp
 * A system of prostitution, credited to Jean O'Hara, where a single prostitute would work three rooms in rotation