Catechism of the Catholic Church §960 — excerpt
The Church is a "communion of saints": this expression refers first to the "holy things" (sancta), above all the Eucharist, by which "the unity of believers, who form one body in Christ, is both represented and brought about" (LG 3).
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.