The authors agree that this surname derives from the ethnic name Longobardo, a form characteristic of southern Italy which did not undergo the reduction to Lombardo proper to the north. The etymology goes back to the Germanic people of the Longobards or Langobards, a Latinization of Langbarden, compounded from langa- ("long") and barda- ("beard"), with the sense of "of the long beard". Both authors note, however, that the surname does not necessarily imply descent from that Germanic people.

E. De Felice explains that between the 10th and 15th centuries the term Longobardo designated one who belonged to Longobardia, the Byzantine theme that covered Puglia and Campania, and in general any inhabitant or native of the south of the Italian peninsula. E. Rossoni agrees with this medieval reading and specifies the present-day geographical distribution: the plural form Longobardi is very widespread in Campania and in Rome, while the singular form Longobardo, fairly rare, is concentrated in the Naples area.