Heresy, derived from the Greek word "hairesis," refers to a belief or opinion that contradicts or challenges established religious doctrines, especially within organized religions like Christianity. Considered as a deviation from orthodox teachings, heresy has historically been condemned and persecuted by religious institutions. Throughout history, many influential figures have been labeled as heretics, such as Galileo Galilei and Martin Luther, due to their opposing views. However, what is considered heresy varies among different religious traditions. The concept of heresy highlights the tension between authority and independent thought, playing a significant role in shaping religious, social, and intellectual movements throughout time.