The term CATACOMB is used to refer to a subterranean CEMETERY or burial chamber, usually consisting of a network of tunnels and chambers. Crypts, graves, cemeteries, tombs, and loculi are all types of catacombs. Crypts are small chambers used for burial, while graves are shallow pits dug into the ground. Cemeteries are large plots of land used for burials, and tombs are larger structures built above ground. Loculi are small niches in the walls of catacombs used for individual burials.