Catechism of the Catholic Church §830 — excerpt
The word "catholic" means "universal," in the sense of "according to the totality" or "in keeping with the whole." the Church is catholic in a double sense: First, the Church is catholic because Christ is present in her.
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: St. Ignatius of Antioch, Ad Smyrn. 8, 2: Apostolic Fathers, II/2, 311 · UR 3 · AG 6 · AG 4