Passover or Pesach is an important, biblically derived Jewish holiday
The Jewish people celebrate Passover as a commemoration of their liberation by God from slavery in Egypt and their freedom as a nation under the leadership of Moses. It commemorates the story of the Exodus as described in the Hebrew Bible especially in the Book of Exodus, in which the Israelites were freed from slavery in Egypt. According to standard biblical chronology, this event would have taken place at about 1300 BCE (AM 2450).
Passover is a spring festival which during the existence of the Jerusalem Temple was connected to the offering of the first-fruits of the barley, barley being the first grain to ripen and to be harvested in the Land of Israel.
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). In Judaism, a day commences at dusk and lasts until the following dusk, thus the first day of Passover only begins after dusk of the 14th of Nisan and ends at dusk of the 15th day of the month of Nisan. The rituals unique to the Passover celebrations commence with the Passover Seder when the 15th of Nisan has begun. In the Northern Hemisphere Passover takes place in spring as the Torah prescribes it: in the month of (the) spring . It is one of the most widely observed Jewish holidays.
Source: Wikipedia