Passover, also called Pesach, is a major Jewish holiday that celebrates the Biblical story of the Israelites escape from slavery in Egypt, which occurs on the 15th day of the Hebrew month of Nisan, the first month of Aviv, or spring. The word Pesach or Passover can also refer to the Korban Pesach, the paschal lamb that was offered when the Temple in Jerusalem stood; to the Passover Seder, the ritual meal on Passover night; or to the Feast of Unleavened Bread. One of the biblically ordained Three Pilgrimage Festivals, Passover is traditionally celebrated in the Land of Israel for seven days and for eight days among many Jews in the Diaspora, based on the concept of yom tov sheni shel galuyot. In the Bible, the seven-day holiday is known as Chag HaMatzot, the feast of unleavened bread .
According to the Book of Exodus, God commanded Moses to tell the Israelites to mark a lamb's blood above their doors in order that the Angel of Death would pass over them (i.e., that they would not be touched by the tenth plague, death of the firstborn). After the death of the firstborn, Pharaoh ordered the Israelites to leave, taking whatever they want, and asked Moses to bless him in the name of the Lord. The passage goes on to state that the Passover sacrifice recalls the time when God "passed over the houses of the Israelites in Egypt". This story is recounted at the Passover meal in the form of the Haggadah, in fulfillment of the command "And thou shalt tell (Higgadata) thy son in that day, saying: It is because of that which the LORD did for me when I came forth out of Egypt."
The wave offering of barley was offered at Jerusalem on the second day of the festival. The counting of the sheaves is still practiced, for seven weeks until the Feast of Weeks on the 50th day, the holiday of Shavuot.
Nowadays, in addition to the biblical prohibition of owning leavened foods for the duration of the holiday, the Passover Seder, at which the Haggadah is read aloud, is one of the most widely observed rituals in Judaism.