Passover, also known as Pesach or Pesah (פסח pesaḥ), is a Jewish holiday, beginning on the evening of the 14th day of Nisan, that commemorates The Exodus and freedom of the Israelites from Ancient Egypt.
The three main applicable mitzvah associated with the holiday are: eating matzoh, or unleavened bread; the prohibition of eating any foods containing leavening during the holiday1; and the retelling of the Exodus (Mitzrayim). In ancient times (until today among the Samaritans) there was a fourth: the offering of a lamb in the evening on the 14th of the Hebrew month of Nisan (also known as Aviv) and the eating that night of the Passover sacrifice. The commandment of retelling the Exodus is fulfilled through a communal ritual called the seder, celebrated on the first two evenings of the holiday (in Israel, only on the first evening). Other customs associated with Passover include eating bitter herbs and other foods specified for the seder meal. While many reasons are given for eating matzoh, the book of Exodus explains that it recalls the bread the Israelites ate at the time of the Exodus: in their rush to leave Egypt, they did not have time for the bread to rise.
