The Passover Seder (; 'order, arrangement'; ) is a ritual feast that marks the beginning of the Jewish holiday of Passover. It is conducted throughout the world on the eve of the 15th day of Nisan in the Hebrew calendar (i.e., at the start of the 15th; a Hebrew day begins at sunset). The day falls in late March or in April of the Gregorian calendar and the Passover lasts for seven days in Israel and eight days outside Israel. Jews generally observe one or two seders: in Israel, one seder is observed on the first night of Passover; many Jewish diaspora communities hold a seder also on the second night. The Seder is a ritual performed by a community or by multiple generations of a family, involving a retelling of the story of the liberation of the Israelites from slavery in ancient Egypt. This story is in the Book of Exodus ("Shemot") in the Hebrew Bible. The Seder itself is based on the Biblical verse commanding Jews to retell the story of the Exodus from Egypt: "You shall tell your child on that day, saying, 'It is because of what the LORD did for me when I came out of Egypt.'" (Exodus 13:8) Traditionally, families and friends gather in the evening to read the text of the Haggadah, an ancient work derived from the Mishnah ("Pesahim" 10). The Haggadah contains the narrative of the Israelite exodus from Egypt, special blessings and rituals, commentaries from the Talmud, and special Passover songs.