Passover is a festival that celebrates the deliverance of Israel from the bondage of the Egyptians. The term is derived from the Hebrew "pasach" which means "to pass over." The Passover begins on the 15th day of the month of Nisan, which typically falls in March or April of the Gregorian calendar. Passover is a spring festival, so the 15th day of Nisan begins on the night of a full moon after the northern vernal equinox.
See BigOven's Passover Recipe Collection