Final answer:
The clergy selling pardons that released people from penalties for their sins is known as the sale of indulgences. This practice was controversial and led to the Protestant Reformation.
Step-by-step explanation:
The practice of the clergy selling pardons that released people from performing penalties for their sins is known as the sale of indulgences. Indulgences were certificates issued by the Church that promised to reduce the time spent in purgatory after death. These indulgences could be earned by performing good deeds or making donations to the Church.
The sale of indulgences was a controversial practice during the 16th century and was a major factor in the Protestant Reformation. Martin Luther, a professor at the University of Wittenberg, protested against the sale of indulgences, arguing that only God could grant forgiveness and that humans had no control over their salvation. Luther's protest eventually led to the formation of separate Protestant denominations.