Easter Sunday celebrates Christ’s resurrection from the dead, following crucifixion. It marks the end of Holy Week, the end of Lent, and the last day of the Easter Triduum (Holy Thursday, Good Friday and Easter Sunday), as well as the beginning of the Easter season of the liturgical year.
Easter always falls on a Sunday between March 22 and April 25, and is tied to the Jewish Passover. The celebration of Passover took place just before the Crucifixion and Resurrection of Christ, so the two holidays have been entwined from the beginning. The word Pasch, originally meaning Passover, came to also mean Easter; the actual Easter date is the first Sunday after the paschal full Moon, on or just after the vernal equinox.