The authors agree that this surname has an anthroponymic origin, derived from a personal name of Germanic root. F. Miranda specifies that it comes from the medieval name Galdus, an Italianization of the Germanic personal name Wald, with the sense of "strong warrior", and that the surname arose from the name of the first bearer. It is considered, for its part, that the root refers to Waldo, with the meanings of "powerful" and also "forest", and that the surname is linked to the Val Cavallina, in the Bergamo area.

Miranda notes that the surname is typical of Cenate Sopra, in the province of Bergamo, and that all its variants derive, directly or indirectly through hypocoristics, from the same medieval Germanic name. He adds that the surname extends through numerous regions of Italy, with presence in Lombardy, Piedmont, the Marche, Calabria, Umbria, Emilia-Romagna, Abruzzo, Lazio, Campania, Tuscany, Veneto and Sicily. The nominal root Galdo also left a trace in several place names of Campania and Molise.