Original: Urbi et orbi is also used at St. Peter's at the Papal inauguration and, on very rare occasions, as the blessing of pilgrims and during the Holy Year (Jubilee).
Simplified: Now Urbi et Orbi refers to a papal address and Apostolic Blessing that is addressed to the City of Rome and to the entire world from the Apostolic Palace in the Vatican. Usually they are only given at Christmas and Easter, but also the first speech of a new pope is Urbi et Orbi, and sometimes one is given to special gatherings of pilgrims in Rome and during Holy Years