Catechism of the Catholic Church §961 — excerpt
The term "communion of saints" refers also to the communion of "holy persons" (sancti) in Christ who "died for all," so that what each one does or suffers in and for Christ bears fruit for all.
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.