It's citizenship transmitted by descent. If you can prove an unbroken Italian-citizen ancestor and that none of them lost or renounced citizenship before passing it on, you may be recognised as Italian by birthright, even if you've never lived in Italy.
It's the main path used by descendants of Italian emigrants in the Americas, Australia, and elsewhere. Rules have tightened recently and some routes (like through female ancestors before 1948) require a court case.
"In Pescara, Lorenzo went through years of Argentine and Italian archive searches to prove his great-grandfather's line. Once the file was complete, the comune issued the recognition and his Italian passport followed."
Recent legal changes have narrowed some iure sanguinis routes. Don't assume what worked for a relative 10 years ago still works today.
Official source
Ministero degli Affari Esteri
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