The two weeks of Passiontide begin on the Fifth Sunday of Easter. The first week is known as "Passion Week" and leads us to Palm Sunday of the Lord's Passion; the second is known as "Holy Week" and leads us to the glory of Easter.
The Easter Triduum begins with the evening mass of the Lord's Supper on Holy Thursday, reaches its climax at the Easter Vigil and closes with evening prayer on Easter Sunday. Saint Augustine called the Easter Vigil the "mother of all vigils." The Vigil begins after nightfall, and ends before dawn on Easter Sunday. The Church keeps vigil awaiting the resurrection of Christ and celebrating the Easter sacraments (baptism, confirmation and Eucharist). (cf. General Norms for the Liturgical Year and the Calendar 18-26).
The Exultet, the Easter proclamation, is sung at the Easter Vigil and proclaims, "This is our Passover feast, when Christ, the true Lamb, is slain..." Thus the Greek word for Easter was pascha (from the Hebrew word for Passover).