Passover or Pesach (; Hebrew: פֶּסַח Pesaḥ/ Peḏaḥ) is a major Jewish holiday and one of the most widely celebrated Jewish holidays. Together with Shavuot and Sukkot, Passover was one of the Three Pilgrimage Festivals (Shalosh Regalim) during which the entire population of the kingdom of Judah made a pilgrimage to the Temple in Jerusalem. Samaritans still make this pilgrimage to Mount Gerizim, but only men participate in public worship.During the existence of the Temple in Jerusalem, Passover was a spring festival that was connected to the offering of the "first-fruits of the barley", as barley was the first grain to ripen and to be harvested in the Land of Israel. The festivals now associated with the Exodus (Passover, Shavuot, and Sukkot) began as agricultural and seasonal feasts but became completely subsumed into the central narrative of Israel's deliverance from oppression at the hands of God.In the Book of Exodus, God helped the Israelites escape from slavery in ancient Egypt by inflicting ten plagues upon the Egyptians before the Pharaoh would release the Israelite slaves. The last of the plagues was the death of the Egyptian first-born. The Israelites were instructed to mark the doorposts of their homes with the blood of a slaughtered spring lamb and, upon seeing this, the spirit of the Lord knew to pass over the first-born in these homes, hence the English name of the holiday.Passover commences on the 15th of the Hebrew month of Nisan and lasts for either seven days (in Israel and for Reform Jews and other progressive Jews around the world who adhere to the biblical commandment) or eight days for Orthodox, Hasidic, and most Conservative Jews (in the diaspora). The rituals unique to the Passover celebrations commence with the Passover Seder when the 15th of Nisan has begun.

— adopted from wikipedia, "pass over", available under CC BY-SA License.