Which term is not a part of the prison slang discussed?

The term "Captain" is not part of the common prison slang discussed, as it typically refers to a rank or position within a correctional facility rather than a colloquial term used by inmates. In prison environments, "Ninja," "Shot Caller," and "Soldier" are all terms that might denote specific roles, behaviors, or hierarchies among inmates.

"Ninja" can refer to someone who moves stealthily or discreetly within the prison, often associated with a sense of cunning or agility in dealings. A "Shot Caller" is a person who has influence and can make decisions regarding actions taken by a group of inmates, often linked to gang hierarchies. "Soldier" typically refers to a member of a gang or someone who carries out tasks for the gang, indicating loyalty and a defined role within the group dynamics.

Thus, while "Captain" is recognized in the correctional officer's hierarchy, it doesn't align with the informal, often coded language used among inmates.