An acronym invented and first seen in common use in the prison's of Los Angeles and Chino in the mid to late 1980's. Meaning,"Just Another Nigger," Often used to describe an average, non-distinct looking African-American male.
Inmate #1: "Yo dude who's that black guy givin' you that funny look?"
Inmate #2: "Who him? Oh, he's a J.A.N."
Black inmate at the same table: " Man.. STFU before I beat yo ass!"