Green’s Dictionary of Slang

(Aus. prison) the Classification Committee; the classification a prisoner receives.

1990		Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Classo. 1. The Classification Committee. This committee assesses prisoners and makes recommendations on their placement in the system. 2. As in ‘A, B, or C classo’, ie the security classification assigned a prisoner.
2005		M.B. ‘Chopper’ Read Chopper 4 168: Imagine me marrying into the classo board.