Catechism of the Catholic Church

Christ's death was a real death in that it put an end to his earthly human existence. But because of the union which the person of the Son retained with his body, his was not a mortal corpse like others, for "it was not possible for death to hold him" and therefore "divine power preserved Christ's body from corruption." Both of these statements can be said of Christ: "He was cut off out of the land of the living," and "My flesh will dwell in hope. For you will not abandon my soul to Hades, nor let your Holy One see corruption." Jesus' Resurrection "on the third day" was the sign of this also, because bodily decay was held to begin on the fourth day after death. (1009, 1683)