The authors differ in the etymology of this surname. F. De Laurentiis proposes that it may derive from Galli or from the nickname galletta, which designates a flat, twice-baked bread of long conservation, used especially as a reserve food in the armed forces, or also the cocoon of the silkworm.

F. Miranda, on the other hand, links it to the hypocoristics —affective and diminutive forms— of the medieval name Gallus (Gallo), which functioned as a byname of a festive or polemical character (rooster, chicken) or an ethnic one, with the Latin meaning of "inhabitant of Gaul" or "native of Gaul", according to E. De Felice. The surname would thus be the transformation into a surname of that byname attributed to the first bearer. Miranda also notes related variants: Galetta, Galetti, Galetto, Galletto, Galletti and Galietti.

The surname is documented in several regions of Italy, with prominent presence in Sicily —especially in the Catania and Messina areas—, as well as in Calabria, Campania, Lombardy, Piedmont, Lazio, Veneto, Puglia and Tuscany.