Bullpen/ˈbʊlpen/ Definition 1 of 3Pro Tip 1/3Baseball Specific Used exclusively in baseball, often unfamiliar outside this context. He's been sent to the bullpen to get ready. Pro Tip 2/3Substitution Area Refers to where players prepare before replacing another on the field. Our closer is in the bullpen getting loose. Pro Tip 3/3Located Near Field The bullpen is typically found adjacent to the playing field for easy access. Fans near the bullpen can watch pitchers warm up.