Catechism of the Catholic Church §948 — excerpt
The term "communion of saints" therefore has two closely linked meanings: communion in holy things (sancta)" and "among holy persons (sancti).
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.