The Catholic Inquisition was a hierarchy of the Catholic Church that targeted those who were thought to be or known to be Protestants or Catholic Reformers. Anyone captured was tortured, questioned, and forced to admit their involvement with the "sinful" religions and repent, or be killed. You were assumed guilty until proven innocent and the goal was reconvert everyone to Catholicism. It was the strongest in Spain, because they owned the Netherlands which was full of protestantism, but also very strong in Italy.
An Inquisition is an official questioning. The catholic Inquisition was when Roman Catholicism was questioned during the Lutheranism, Calvinism, Zwinglyism age, after the printing of the bibles for people to read, not just the Catholic hierarchy. People began to realize the corruption in the Catholic system, such as the need of money from the prayer goers, and how it was necessary to give money to the church in order to get in heaven.