Normally in stock yards there are whole herds of cattle in large fenced in areas, However the "bulls" are separated from the heffers and placed in a smaller confined area know as the bullpen. The term has come to mean any smaller area of confinement. Prisoners awaiting a hearing are kept in the "bullpen" in the basement of the courthouse. The senior staff meeting is held in the "bullpen" otherwise know as the conference room. In baseball it is the "smaller" remote area, away from the playing field, where the relief pitcher stays and warms up. (Practices)