Passover, also known as Pesach, is an eight day Jewish holiday (seven days in Israel) that commemorates the exodus and freedom of the Israelites from Egypt.
The term passover comes from the fact that God killed all Egyptian firstborn sons, but "passed over" the Jews; this is described in Exodus, or the Second Book of Moses.
The two main commandments associated with the holiday are: eating matzoh, or unleavened bread; and the prohibition of eating any foods containing leavening during the holiday. In ancient times there was a third: the offering on the 14th of the Hebrew month of Nisan and the eating that evening of the Passover sacrifice. The commandments have since combined into a special Passover feast called the seder, celebrated on the first two evenings of the holiday (but only on the first evening in Israel). Other customs associated with Passover include eating bitter herbs and other foods at the seder celebration. While many reasons are given for eating matzo, the most popular tradition is 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.
Before the holiday begins, observant Jews will remove and discard all food with leavening from their households, doing a thorough job, so that not even a crumb remains. Throughout the holiday, they will eat no leavened food, replacing breads, pastas, and cakes with matzoh and other specially prepared foods.
Passover is a family holiday and a happy one. The first night is the most imporant, followed by the second night. It is traditional for a Jewish family to gather on both these nights for a special dinner called a seder where the story of the Israelite exodus from Egypt is retold by the reading of the story of the Exodus from Egypt, the Haggadah.
Although the Christian Holy Week occurs around the same time as Passover, Passover rarely occurs during Easter. This is because the Jewish holidays follow a lunar calendar, and Christian holidays follow the Gregorian calendar. Not exactly correct. The Christian calendar is designed so that Easter nearly always falls out during the week of passover or immediately after. When it doesn't, it is simply an error in the Christian calendar.
Pesach commemorates the liberation of the Israelites from Egypt. The first seder is on the 14th of Nisan. On the night of the 15th, the second seder is held (except in Israel). On that night Jews start counting the Omer; The omer is a counting down of the days from the time they left Egypt, until the time they arrived at Mount Sinai. This 49 day ("seven weeks") period of counting is known as the sefirah, and bridges Pesach (Passover) and Shavuot (The Feast of Weeks). This period is defined by the Torah as the period for Jews to bring special offerings to the Temple In Jerusalem; According to Judaism, this marks physical the spiritual connection between Pesach and Shavuot.