Bullpen

Wikipedia - "In baseball, the bullpen (or simply the pen) is the area where relief pitchers warm-up before entering a game. Depending on the ballpark, it may be situated in foul territory along the baselines or just beyond the outfield fence. Also, a team's roster of relief pitchers is metonymically referred to as "the bullpen". These relievers usually wait in the bullpen when they have yet to play in a game, rather than in the dugout with the rest of the team. The starting pitcher also makes his final pregame warmups in the bullpen. Managers can call coaches in the bullpen on an in-house telephone from the dugout to tell a certain pitcher to begin his warmup tosses."
Wikipedia