Green’s Dictionary of Slang

boof n.

[? buttfuck v. (1)]

(US prison) contraband hidden in the rectum.

[US]Other Side of the Wall: Prisoner’s Dict. July [Internet] Boof: Contraband concealed in the rectum.
[US]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.