An internment camp is a form of prison.
Dominion internment camps are designed to hold enemies of the Dominion. The law of these camps are that "there is no release, no escape... except death." Prisoners are sheltered in barracks and are free to move about the compound. The design of the internment camp is so to reinforce those rules – as the camps are contained in an atmospheric dome, in which leaving, even for an instant, will cause immediate death. These camps are not protected with shields. (DS9: "In Purgatory's Shadow")