The Justice Zone, or Justice Field, is a reality-altering energy field contained within the holding cells of Justice World, a space prison visited by the boys from the Dwarf in the Series IV episode "Justice".
If anyone attempts a crime within the Justice Zone, the consequences happen to the perpetrator instead of their victim. Lister learns this hard way when, at Rimmer's insistence, when he tries to set fire to Rimmer's bed sheets and instead sets fire to his own jacket. The thinking is that once the prisoners have served their sentences, being forced to live within the law will have become second nature
Other examples include if a prisoner steals something, something of theirs goes missing. If someone attacks someone else, they feel the pain of their own blows and are shot/stabbed by their own weapons. In a deleted scene, "Litter Birds" drop their "cargo" on any who litter in the botanical gardens, which Lister did accidentally. ("Justice", Series IV)
The Justice Zone technology was later utilized in the creation of the Karma Drive, which propelled a ship - the SS Samsara - and rewarded good behavior while punishing bad behavior based on the moral code that had been programmed into the drive. ("Samsara", Series XI)