that is when the Torah tells us to conduct the Seder (Exodus ch.12).
In Israel, the Seder is on the first night of Passover. Outside Israel, Orthodox and some Conservative Jews celebrate Seders on the first two nights of Passover. Most other Jews have a Seder on only the first night, though some may also have Seders on the first two nights of Passover.
The Seder Plate is a special plate for holding the symbolic foods used during the seder. Pieces of the symbolic foods are distributed to everyone during the course of the seder. Traditionally, the person leading the seder is the only one with a Seder Plate. However if there are many guests, additional Seder Plates can also be set on the table.
night of passover
The religious ceremony held on the first two nights of Passover outside of Israel (1st night only in Israel) is called a Seder. The word Seder means 'order'.
The basic requirements of the seder were announced and taught to the Jewish people immediately BEFORE the Exodus from Egypt, when it was commanded that the occasion was to be recalled annually. Thus the first seder took place on the night of the Exodus. See Exodus 12, verses 1-20.
The Seder.
The Seder is on the first night of Passover which is the 15th of Nissan on the Jewish calendar. It corresponds to a different date each year on the Gregorian calendar. But is usually in the beginning to mid April.
The Seder is eaten the first two nights of Passover outside of Israel, and the first night in Israel.
The first seder happened on the eve of the Exodus from Egypt. Tradition puts the date at 1312 BCE.
biannual actually, the 1st and 2nd night
The ritual foods at a Passover seder are Matzah (unleavened bread), Maror (bitter herbs), Karpas (a green vegetable, usually parsley), Beitzah (a roasted, hard boiled egg), Haroset (a mixture of apples, nuts, cinnamon, wine) and Z'roa (a shank bone, usually represented by a turkey neck or a beet). Four cups of wine are traditional as well. The main course can be almost anything, as long as it complies with Passover dietary laws.
The Passover dinner that is eaten the first night of Passover in Israel, and the first two nights outside of Israel is called the Seder