Green’s Dictionary of Slang

1. (US prison) contraband hidden in the rectum.

2000		Other Side of the Wall: Prisoner’s Dict. July 🌐 Boof: Contraband concealed in the rectum.
2011		G. Hayward Corruption Officer [ebk] cap. 19: After having the inmate searched, drugs were found in between his butt cheeks as he was attempting to commit an act called boofing. Boofing is when an inmate secretes a hidden item from inside of his rectum.

2. (UK black) £1, thus money.

2005

Jade LB Keisha the Sket (2021) 38: ‘I made some cash money [...] 300 boof ’ [...] He handed me a stack of notes’.