What is the Papal Schism?

Answer 1

When a pope was being elected in the 1300s, the people of Rome rioted to ensure an Italian was elected. The pope they chose turned out not to be all that good at it, so a lot of the cardinals went back to Avignon and elected another pope, dividing the church.

Answer 2

The First Great Schism (break-up) in Christianity (AD 1054)

or
The Great Schism of the Papacy in (1378 – 1417)

early in the year 1377, Pope Gregory XI ended the Babylonian Captivity (when the popes lived in Avignon under the thumb of the French king) by freely returning to Rome. Unfortunately, his return did not bring about the looked-for results, because Gregory XI died a year later, and a situation much worse than the Babylonian Captivity emerged.
The return of Gregory XI to Rome created a split in the College of Cardinals
between the French party and the Italian party. Upon his death in 1378, the Italian party of cardinals elected Urban VI (reigned 1378 - 1389 ), while the French party chose Clement VII (antipope 1378 – 1394). Now there were two popes: Urban VI, who held court in Rome, and Clement VII who held court at Avignon. Each rival pope was elected by cardinals; each claimed to be the legitimate successor of St. Peter; and each denounced, excommunicated and anathematized (cursed) the other.
Thus, from 1378 to 1417 (a period of 39 years), western European Christendom was divided between two rival popes. This period came to be known as the Great Schism, and is not to be confused with the schism of 1054 between the eastern and western wings of the Church. In general, northern Italy, most of Germany, England and the Scandinavian countries followed the pope in Rome; while France, Spain, Scotland and southern Italy followed the pope at Avignon.
This state of affairs was not only hurting the papacy, it was hurting the entire Church. The clamor for reform grew. In 1409, a council was held in Pisa, which deposed the two popes and elected another. But the pope at Avignon and the pope in Rome refused to accept the decision of the council. Hence, for several more years, there came to be three popes excommunicating one another. Finally, in 1417, the Council of Constance elected an Italian cardinal who became Martin V (reigned 1417 - 1431). The three rival popes gave up their struggle and decided to give Martin V their support. Thus, the Great Schism ended, but the deep wound it inflicted to Christianity continued to throb for many, many years. It intensified the call for reform, which culminated in the eruption of the Protestant Reformation in the 16th century.