Catechism of the Catholic Church §2390 — excerpt
In a so-called free union, a man and a woman refuse to give juridical and public form to a liaison involving sexual intimacy.
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: FC 81