Easter commemorates the resurrection of Jesus Christ laid down by the Bible, the third day after his passion. The solemnity begins on Easter Sunday, which for Catholics mark the end of fasting of Lent, and lasts for eight days (Easter week, or week or radiant, or week of eight Sundays).
“Passover”, from the popular Latin pascua, alteration (by influence of pascua “food”, the verb pascere “to feed”) of ecclesiastical Latin Pascha, from the Greek πάσχα / páskha, itself borrowed from the Hebrew פסח “he went [over],” where “path” is the name of the Jewish holiday that commemorates the exodus from Egypt. According to the Gospels, it is during this Jewish holiday that took place the resurrection of Jesus; that is why the name was taken to mean the Christian holiday.
The phrase “Orthodox Easter” is sometimes used to refer to this party when it is celebrated by the Orthodox on a date different from the date the Western Churches. Some languages distinguishe “the” original Passover and the Christian Easter. The first commemorates the exodus from Egypt by a ritual meal that is also called “the Passover.” The Christian holiday is manifold. It commemorates both the exodus from Egypt, the Eucharistic institution during the Passover meal, the crucifixion of Christ and rest in the tomb for three days, his resurrection passage from death to life, and the new creation inaugurated the third day.
There is also a Quartodecimanism practiced by some Christian churches: some religious groups, such as the Church of God (Seventh Day), some Seventh Day Baptists or Jehovah’s Witnesses, choose to perform the ceremony in accordance with the Jewish Passover.
Translated and adapted from Wikipedia.