Grahv was the home planet of the Grahvians. During the Last Great Time War it was attacked by the Daleks, who built a base in the Grallian Hills.
The Time Lords placed it in a time lock. (AUDIO: The War Valeyard)
The Eighth Doctor mentioned the Valeyard's planet as a place, like the Gulf of Ithon, where the walls of reality were weak. (AUDIO: Restoration of the Daleks)