A prison gang is an inmate organization that operates within a prison system. It has a corporate entity and exists into perpetuity. Its membership is restrictive, mutually exclusive, and often requires a lifetime commitment. Prison officials and others in law enforcement use the euphemism "security threat group" (or "STG"). The purpose of this name is to remove any recognition or publicity that the term "gang" would connote when referring to people who have an interest in undermining the system.