Nightmare Child

Nightmare Child was an unknown event or thing, that the Time War ran into during the first year of battle. Davros' command ship flew into the "jaws" of the Child, despite the war being Time locked, Dalek Caan managed to an emergency temporal shift. (DW: Evolution of the Daleks) He arrived in the middle of the battle and saved Davros from the "jaws" of the Nightmare Child (DW: The Stolen Earth)

It has not yet been precisely explained what a/the "Nightmare Child" actually was. Though it seems likely that it was some kind of black hole or other spacial anomaly.