bull pen

noun
1.
Baseball.
  1. a place where relief pitchers warm up during a game.
  2. the relief pitchers on a team.
2.
Informal.
  1. a large cell or room, usually next to the courtroom, where prisoners are temporarily held.
  2. a large room in an office occupied by many employees.
3.
any temporary or crowded quarters, as sleeping quarters in a lumber camp.
4.
a pen for a bull or bulls.
Also, bullpen.
Origin
1800-10, Americanism for def 4; 1920-25 for def 1
British Dictionary definitions for bullpen

bullpen

/ˈbʊlˌpɛn/
noun
1.
(US, informal) a large cell where prisoners are confined together temporarily
2.
(baseball) a part of a baseball field where relief pitchers warm up
Word Origin and History for bullpen
n.

also bull-pen, 1915, in the baseball sense, from bull (n.1) + pen (n.2); perhaps from earlier slang meaning "temporary holding cell for prisoners" (1809). Bullpen also was the name of a baseball-like game played in U.S. late 19c.

Slang definitions & phrases for bullpen

bullpen

noun
  1. A cell or secure area where prisoners are kept temporarily; tank: We're in the bullpen waiting to go to court (1880s+)
  2. A military stockade; military prison (1900+)
  3. A usually enclosed area where pitchers practice and warm up: The bullpen's getting active now (1915+ Baseball)
  4. The relief pitching staff of a baseball team: They've got starters but no bullpen (Baseball)
  5. bunkhouse (1930+ Loggers)
  6. living room, lounge, etc, where a girl's escorts and suitors are appraised by friends and family (1940s+ Students)

[baseball sense perhaps fr a boys' game called bullpen, attested fr 1857, in which opponents lined up in a rectangle and threw balls at each other; similarly, the pitchers in the bullpen are vulnerable to being hit by thrown and hit balls]