A movement within the ranks of Protestantism, originating in a reaction against the prevailing laxity of morals in the 17th century.
Its leader was Philipp Jakob Spener (1635-1705), an Alsatian who studied at Geneva.
Through his sermons Spener sought to influence his hearers to a devout life, but realising that sermons alone were not sufficient he formed his Collegia pietatis (whence the name of the movement), and sought by means of private meetings and spiritual exercises to further this purpose.
On the practical side, Pietism did much to develop charitable and missionary enterprise.
Unfortunately, in many of its later adherents it degenerated into fanaticism.
New Catholic Dictionary