Urbi et Orbi ("to the City of Rome and to the World") was a standard opening of Roman proclamations. The term is now used to denote a papal address and Apostolic Blessing that is addressed to the City of Rome and to the entire world.

The blessing takes place at each Easter and Christmas celebration in Rome from the central loggia of St. Peter's Basilica, at noon. Part of the urbi et orbi blessing is the remission of all temporal punishment due to sin through a plenary indulgence attached to the Papal blessing.

The blessings at Christmas and Easter are broadcast throughout the world by the European Broadcasting Union. The indulgence and remission of venial sins is not only granted to the people in St. Peter's Square but also to Catholics watching the ceremony on television and listening on radio

via Wikipedia.