Holy Communion, because by this sacrament we unite ourselves to Christ, who makes us sharers in his Body and Blood to form a single body. We also call it: the holy things (ta hagia; sancta) - the first meaning of the phrase "communion of saints" in the Apostles' Creed - the bread of angels, bread from heaven, medicine of immortality, viaticum....
Source: Catechism of the Catholic Church (Vatican.va)