What was the counter-reformation?

The Counter-Reformation was a period of spiritual, moral, and intellectual revival in the Catholic Church in the 16th and 17th centuries, usually dated from 1545 the opening of the Council of Trent to 1648 the end of the Thirty Years' War. While it is normally seen as a reaction to the Protestant Reformation, the Counter-Reformation has roots going back to the 15th century, and is therefore sometimes called the Catholic Revival or the Catholic Reformation and occasionally the Catholic Counter-Reformation.