The authors agree that the surname derives from the Germanic name Warin, Latinized as Guarinus and Varinus, with the meaning "to protect, to defend". It is a name of Lombard tradition, documented from the 7th and 8th centuries. F. De Laurentiis specifies that Warin could function both as an autonomous name and as a shortened hypocoristic of compounds with that same element as first component. V. Blunda adds that the root warin is one of the most productive components of ancient Germanic anthroponymy, and appears as the first element in compounds such as Garibaldo, Garimberto or Guarnerio.

A. Bongioanni notes that the name was popularized by the romance Guerino il Meschino, documents the form Warinus in a text of the year 765 from Santa Agata in Tempagnano, and warns that some variants may be shortenings of Nascinguerra or Vinciguerra, by analogy with Guerra. F. Miranda also Latinizes the form as Guerinus and groups under this origin a set of variants including Guarin, Guarini, Guerin, Guerini, Guerrini and Guerrisi.

As for geographical distribution, the authors agree that the surname is found throughout the Italian peninsula, with the greatest concentration in southern Italy, especially in the Naples area. Miranda details a presence in Campania, Sicily, Apulia, Lombardy, Lazio, Piedmont, Basilicata, Tuscany and Emilia-Romagna. In Sicily, Blunda places it as a surname of Germanic root well established on the island, while Miranda indicates a presence in all its provinces, with notable cores in the Palermo, Agrigento, Catania and Messina areas.