The surname Orrù is of toponymic and nickname origin, linked to the Sardinian sphere. On this point E. De Felice and E. Rossoni agree, relating it with the Sardinian term orrù ("bramble", "thorny scrub"), derived from the Latin rubus, used both to designate places characterized by this vegetation and to form nicknames linked to the natural environment.

E. De Felice interprets it mainly as derived from local place names formed from this term, while E. Rossoni adds that it could also have originated as a byname or, in some cases, be linked with specific places such as Villa d'Orri, although its presence is earlier than that place name. He also documents the surname widely in medieval Sardinia, which confirms its antiquity and its consolidation as a hereditary surname on the island.