The authors agree that this surname derives from the medieval Latin name Bullus or Bulla, or from variants arisen by aphaeresis of the Lombard name Rebollus, or from a nickname linked to the term bulla. E. Rossoni notes that the name is documented in an epitaph and also in the Condaghe di Santa Maria di Bonarcado, a register of the 11th–13th centuries from Sardinia.

The term bulla admits several meanings. F. Miranda details, citing Caracausi, that it can refer to a "soap bubble", to a "pustule" or to the "seal of a pontifical or imperial document"; and he adds that in the Sicilian dialect buddra designates a blister formed by the wear of the skin. V. Blunda notes that in Sicilian the equivalent dialectal word is bùdda, with the sense of "blister from friction", frequent as an injury among manual field workers, which would explain its use as a nickname.

As for its geographical distribution, Rossoni indicates that the surname presents specific areas of presence in the Brescia area, in Rome, in the Catania area and in northern Sardinia. The forms Bulli and Bullo appear respectively in the Florence and Rome areas, and in Venice and its surroundings.