Easter is the celebration of Christ's resurrection from the dead. It is celebrated on Sunday, and marks the end of Holy Week, the end of Lent, the last day of the Easter Triduum (Holy Thursday, Good Friday and Easter Sunday). Following Easter Sunday, the season of Easter begins and lasts for seven weeks, ending with Pentecost.
Jesus' resurrection marks the triumph of good over evil, sin and death. It is the singular event which proves that those who trust in God and accept Christ will be raised from the dead.
Since Easter represents the fulfillment of God's promises to mankind, it is the most important holiday on the Christian calendar.
The Paschal Greeting is an Easter custom. In place of, "Hello," or an equivalent greeting, adherents greet each other by announcing, "Christ is Risen!". The response to this is, "He is Risen Indeed".
This greeting can be linked to the following excerpts from the Gospels of Matthew, Mark, and Luke:
Matthew 27:64
Matthew 28:6-7
Mark 16:6
Luke 24:6
Luke 24:34