Great Schism

During the Intuitive Revelation, (PROSE: Cat's Cradle: Time's Crucible) the Great Schism was an event that befell the planet Gallifrey long before the Gallifreyans took their position as Time Lords. It involved a war between the forces loyal to Rassilon and the female priesthood of the Pythia. The ruling matriarchy was defeated and banished from Gallifrey, but not before the last Pythia cursed the Gallifreyans with sterility. This led to a change in their reproduction: because their women could no longer give birth, the Looms were created. (PROSE: Lungbarrow)

Behind the scenes
In the real world, the phrase "" most commonly refers to major splits within or from the Catholic Church in the 11th and 14th centuries.