The authors agree that this surname is typical of the region of Campania, with presence also in the Foggia area, and that it derives from dialectal nicknames influenced by the Spanish term fierro ("iron"), linked to the trade of blacksmith or to the work with that metal.

F. Miranda broadens the geographical panorama and notes that the surname is spread in almost all the regions of Italy, among them Campania, Puglia, Lombardy, Piedmont, Lazio, Molise, Emilia-Romagna, Basilicata and Liguria. In Sicily it appears in a specific way in the Messina, Catania, Palermo and Syracuse areas and in the locality of Centuripe, in the Enna area. Miranda also specifies that the original nicknames were linked to the work of the first bearer of the surname in the extraction or elaboration of iron.