Nazi concentration camps were work camps that were run by Hitlers SS police. These camps were set up to hold prisoners while torturing them or using them for work. These are not the same as extermination camps which were used for the mass killings of Jews.
Most prisoners were anything labeled "undesirables" such as German Communists, Socialists, Social Democrats, Jehovah's Witnesses, homosexuals, and persons accused of 'asocial' or socially 'deviant' behavior by the Germans (criminals), Jews, Soviets, disabled people, and clergymen.
