The authors agree that this surname is typical of Sicily, with a presence concentrated in the Agrigento and Caltanissetta areas. F. Miranda specifies that it also appears in almost every Sicilian province, with isolated records in the Enna area —specifically in the municipalities of Barrafranca, Aidone, Valguarnera Caropepe, Piazza Armerina, Troina, Pietraperzia and Regalbuto—, as well as in other regions of northern and central Italy: Lombardy, Piedmont, Lazio, Tuscany, Veneto, Liguria, Emilia-Romagna, Friuli-Venezia Giulia and Campania.

As for its origin, both authors suggest that the surname could derive from the aphaeresis of names such as Miguel. Miranda adds a second hypothesis: a derivation from the Arabic ghaly, meaning "toilsome" or "burdensome". E. Rossoni further notes the existence of documentary records of the surname in the form Guelus going back to the 16th century.