The scholars consulted agree that this surname derives from the medieval personal name Orso, a continuation of the imperial Latin nomen Ursus, meaning "bear." E. De Felice notes that the name underwent a notable expansion in the early Middle Ages, favoured by the prestige of Germanic names built around the same animal — a symbol of strength and valor — and that it could also have been recreated directly from the Romance form oso. R. Brondolo interprets it as a Latin auspicious name carrying the wish "may you be strong as a bear." It is also recorded as a nickname applied to a strong person.

E. Rossoni documents the use of the personal name Orso in legal deeds from 722 and 762, during the Lombard period, and details the geographic distribution of the related surname forms. Orsi is characteristic of Lombardy, Emilia-Romagna, the area of Alessandria, Liguria, and upper Tuscany. Orso has an important concentration in Veneto, with further presence in Piedmont and Campania. Orsoni is specific to Bologna and its surrounding area.

De Felice further notes that the Latinizing variant Urso predominates in southern Italy, where patronymic forms with the prefix D' and various compound forms are also characteristic. A Slavic-type form with the suffix -ič is recorded in Friuli-Venezia Giulia. F. De Laurentiis adds that the surname is found throughout Italy, with greater frequency in Emilia-Romagna.