Indulgences were a practice in the Catholic Church during the Middle Ages, where individuals could reduce their time in purgatory by performing certain actions, such as prayers or charitable deeds. They were often sold, leading to widespread criticism and the perception that they allowed people to buy their way into heaven. The sale of indulgences became a significant issue during the Reformation, particularly with figures like Martin Luther who opposed the practice. This controversy contributed to the split in the Christian Church and the rise of various Protestant denominations, which rejected the concept of indulgences altogether.