Green’s Dictionary of Slang

fridge n.

1. (Aus.) a prison.

[Aus]Baker Aus. Lang.

2. (N.Z. prison) the rectum, in the context of smuggling.

[NZ]D. Looser Boobslang [U. Canterbury D.Phil. thesis] 74/1: fridge n. the rectum, referring to the way it is made use of by some inmates to conceal contraband.