Ar-Rabb is the owner who has full authority over his property. Ar-Rabb, linguistically means, the master or the one who has the authority to lead. All of these meanings are correct for Allah. When it is alone, the word Rabb is used only for Allah. As for other than Allah, it can be used to say Rabb Ad-Dar, the master of such and such object. Further, it was reported that Ar-Rabb is Allah's Greatest Name.