The phrase The Great Schism is used to mean two different things:
- The East-West Schism of 1054 was the separation of the Eastern Orthodox Church and Western ("Roman Catholic") branches of the Christian Church.
- The Western Schism (1378-1417) was an argument within the Roman Catholic Church resulting in French cardinals electing an "antipope" (Clement VII of Avignon, France) in order to dispute the authority of the recently elected Pope Urban VI. In 1409, a third antipope (John XXIII) existed in Pisa, Italy.  This and other controversies set the stage for the Protestant Reformation.
- Catholic Encyclopedia 1913, http://www.newadvent.org/cathen/13539a.htm