Counter-Reformation: The Counter-Reformation refers to the period of Catholic revival and reform initiated in response to the Protestant Reformation, marked by efforts to address corruption and reaffirm Catholic doctrine.
Justification: Justification is a theological concept regarding how a person can be made righteous before God, which was a central point of contention between Catholic and Protestant beliefs during the Reformation.
Indulgences: Indulgences were grants made by the Catholic Church that reduced the punishment for sins, a practice heavily criticized by Reformers like Martin Luther.