(slang) The anus or vagina (in the context of them being used to hide and smuggle items).
2014 April 24, Byker, “Now that's what I call concealed carry”, in alt.fan.rush-limbaugh[1] (Usenet):
A Tennessee teenager was arrested and brought to jail with a loaded revolver hidden in her vagina Monday. […] Archer isn't the first woman to use her prison pocket to smuggle a firearm into jail, and she certainly won't be the last.
2015 August 13, David VanDyke, Ryan King, Apocalypse Austin: Plague Wars Book 4 (Plague Wars)[2], Reaper Press, →ISBN:
Skull emptied his pockets. Terry then searched him, roughly. “You sure you don't want to check my prison pocket? I might have something special in there for you to pull out.” “We'll pass,” Terry said, pulling out a pair of handcuffs.
2021 January 28, K. Pimpinella, Nexus Point[3], FriesenPress, →ISBN, →OCLC, page 126:
“Shove it up your prison pocket, Perry!”
Used other than figuratively or idiomatically: seeprison, pocket.
