Persecution is the systematic mistreatment of an individual or group by another individual or group. The most common forms are religious persecution, ethnic persecution and political persecution, though there is naturally some overlap between these terms. The inflicting of suffering, harassment, imprisonment, internment, fear, or pain are all factors that may establish persecution, but not all suffering will necessarily establish persecution. The suffering experienced by the victim must be sufficiently severe. The threshold level of severity has been a source of much debate.