Green’s Dictionary of Slang

(N.Z. prison) an excl. that follows the completion of the muster or body count, at which time it is safe to circulate contraband.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 23/1: bodycount! int. an expression used by inmates after lock to let their fellow inmates know that the officers have finished their evening muster (or body count) and that it is now safe to send contraband to one another.