The authors agree that the surname derives mainly from Italian place names that bear that name. F. Miranda notes that the localities of origin are found in the provinces of Teramo, Catanzaro, L'Aquila and Enna, and indicates that its variants (Gagliani, Galiani, Galiano) could also derive from the gens Gallia or from the Latin name Gallus. Miranda documents an especially intense presence in Sicily, with rooting in practically all its provinces, and also in Lombardy, Piedmont, Campania, Lazio, Calabria, Tuscany, Emilia-Romagna, Liguria and Puglia.

R. Brondolo proposes an additional etymological route: the term gallius, with the sense of "multicoloured like a rooster", which would link the surname with that bird. Brondolo also mentions a place name Gagliano located in the area of Cividale del Friuli, in the northeast of Italy, as a possible independent point of origin for the north of the country.