Catechism of the Catholic Church §1031 — excerpt
The Church gives the name Purgatory to this final purification of the elect, which is entirely different from the punishment of the damned. The Church formulated her doctrine of faith on Purgatory especially at the Councils of Florence and Trent.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: Council of Florence (1439): DS 1304 · Council of Trent (1563): DS 1820 · (1547): 1580 · see also Benedict XII, Benedictus Deus (1336): DS 1000 · St. Gregory the Great, Dial. 4, 39: PL 77, 396