The authors agree that the surname derives from the place name Gagliano, a name shared by several Italian localities. E. Rossoni mentions those located in the provinces of Teramo, Catanzaro, L'Aquila, Lecce and Enna, and also notes as a possible origin the Roman Gens Gallia. F. De Laurentiis broadens that list and also includes localities in the provinces of Udine and Macerata, among others.

Rossoni documents an early trace of the transformation into a surname in Naples, in a deed of 1547, and highlights that in the 18th century the master luthier Alexander Gaglianus was famous in that city. He also notes that both Gagliani and the variant Galiani are extremely rare surnames peculiar to Naples, while Gagliano seems characteristic of Sicily and Galiano presents a scattered presence in southern Italy and in Sicily.