The authors agree that the surname derives from the medieval name Galassus, a Latinization of Galeazzo. E. Rossoni documents this name already in the year 1400 in Sarezzo, in the Brescia area, and in the Crotone area, where a certain Galassus de Tarcia appears. Rossoni also records an early trace of its transformation into a surname in Comiso, in the Ragusa area, during the 16th century, through the sculptor Natale, known as Galazzo.

F. De Laurentiis offers a complementary perspective: he notes that the base of the surname is a nickname coming from the old Venetan term galasso, with which someone was designated "gallant, of gentle and ceremonious manners, especially towards women; a suitor, elegant".

As for its geographical distribution, Rossoni notes that Galassi is concentrated mainly in centre-northern Italy, with prominent presence in Emilia-Romagna and the Marche. Related forms such as Galasso predominate in the continental centre-south, with presence also in Piedmont, Lombardy and Veneto. Galazzi presents zones in the Bologna area and in Lombardy; Gallazzi is peculiar to Busto Arsizio and the Varese and Milan area; while Gallazzo and Galazzo turn out to be very rare forms, with scattered records in Piedmont and the Ragusa area respectively.