The Derby delle Isole ("Derby of the Islands") is an Italian Serie A and Serie B derby between the two football clubs U.S. Città di Palermo and Cagliari Calcio. It is played twice a year, unless the two sides do not play in the same division that season.
Derby delle Isole translates in English to the Derby of the Islands, those islands being Sardinia and Sicily.
References
Derby delle Isole Wikipedia(Text) CC BY-SA