In its most basic form, the term “bullpen” refers to the physical location where the team’s relief pitchers warm up prior to entering the game. Typically, this area is a fenced-off section beyond the outfield fence, although occasionally it can be found in foul territory down the outfield lines. From here, this physical location has over time lent its name to two related terms. By metonymy — a figure of speech in which one thing takes on the name of something closely related to it — it has become the collective name for a team’s group of relief pitchers (for example, the Yankees’ bullpen).
The Civil War roots of the bullpen
